diff --git a/src/app/[locale]/settings/providers/_components/forms/provider-form/provider-form-context.tsx b/src/app/[locale]/settings/providers/_components/forms/provider-form/provider-form-context.tsx
index 7b89a5dbe..9f9c890a2 100644
--- a/src/app/[locale]/settings/providers/_components/forms/provider-form/provider-form-context.tsx
+++ b/src/app/[locale]/settings/providers/_components/forms/provider-form/provider-form-context.tsx
@@ -22,7 +22,8 @@ export function createInitialState(
   }
 ): ProviderFormState {
   const isEdit = mode === "edit";
-  const sourceProvider = isEdit ? provider : cloneProvider;
+  const raw = isEdit ? provider : cloneProvider;
+  const sourceProvider = raw ? structuredClone(raw) : undefined;
 
   return {
     basic: {
@@ -322,11 +323,13 @@ export function providerFormReducer(
       return { ...state, ui: { ...state.ui, showFailureThresholdConfirm: action.payload } };
 
     // Reset
-    case "RESET_FORM":
+    case "RESET_FORM": {
+      const fresh = structuredClone(defaultInitialState);
       return {
-        ...defaultInitialState,
-        ui: { ...defaultInitialState.ui, activeTab: state.ui.activeTab },
+        ...fresh,
+        ui: { ...fresh.ui, activeTab: state.ui.activeTab },
       };
+    }
 
     // Load provider data
     case "LOAD_PROVIDER":
diff --git a/tests/unit/dashboard/provider-form-clone-deep-copy.test.ts b/tests/unit/dashboard/provider-form-clone-deep-copy.test.ts
new file mode 100644
index 000000000..d5a0932ba
--- /dev/null
+++ b/tests/unit/dashboard/provider-form-clone-deep-copy.test.ts
@@ -0,0 +1,158 @@
+import { describe, expect, it } from "vitest";
+import { createInitialState } from "@/app/[locale]/settings/providers/_components/forms/provider-form/provider-form-context";
+import type { ProviderDisplay } from "@/types/provider";
+
+function makeProvider(overrides?: Partial<ProviderDisplay>): ProviderDisplay {
+  return {
+    id: 1,
+    name: "TestProvider",
+    url: "https://api.example.com",
+    maskedKey: "sk-****1234",
+    isEnabled: true,
+    weight: 1,
+    priority: 0,
+    groupPriorities: { groupA: 10, groupB: 20 },
+    costMultiplier: 1.0,
+    groupTag: "groupA,groupB",
+    providerType: "claude",
+    providerVendorId: null,
+    preserveClientIp: false,
+    modelRedirects: { "claude-3": "claude-3.5" },
+    allowedModels: ["claude-3", "claude-3.5"],
+    mcpPassthroughType: "none",
+    mcpPassthroughUrl: null,
+    limit5hUsd: null,
+    limitDailyUsd: null,
+    dailyResetMode: "fixed",
+    dailyResetTime: "00:00",
+    limitWeeklyUsd: null,
+    limitMonthlyUsd: null,
+    limitTotalUsd: null,
+    limitConcurrentSessions: 0,
+    maxRetryAttempts: null,
+    circuitBreakerFailureThreshold: 3,
+    circuitBreakerOpenDuration: 60000,
+    circuitBreakerHalfOpenSuccessThreshold: 2,
+    proxyUrl: null,
+    proxyFallbackToDirect: false,
+    firstByteTimeoutStreamingMs: 30000,
+    streamingIdleTimeoutMs: 60000,
+    requestTimeoutNonStreamingMs: 120000,
+    websiteUrl: null,
+    faviconUrl: null,
+    cacheTtlPreference: null,
+    context1mPreference: null,
+    codexReasoningEffortPreference: null,
+    codexReasoningSummaryPreference: null,
+    codexTextVerbosityPreference: null,
+    codexParallelToolCallsPreference: null,
+    anthropicMaxTokensPreference: null,
+    anthropicThinkingBudgetPreference: null,
+    anthropicAdaptiveThinking: {
+      effort: "high",
+      modelMatchMode: "specific",
+      models: ["claude-opus-4-6"],
+    },
+    geminiGoogleSearchPreference: null,
+    tpm: null,
+    rpm: null,
+    rpd: null,
+    cc: null,
+    createdAt: "2025-01-01T00:00:00.000Z",
+    updatedAt: "2025-01-01T00:00:00.000Z",
+    ...overrides,
+  } as ProviderDisplay;
+}
+
+describe("createInitialState deep-copy safety", () => {
+  describe("clone mode", () => {
+    it("modelRedirects is a distinct object with equal values", () => {
+      const source = makeProvider();
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.modelRedirects).toEqual(source.modelRedirects);
+      expect(state.routing.modelRedirects).not.toBe(source.modelRedirects);
+    });
+
+    it("allowedModels is a distinct array with equal values", () => {
+      const source = makeProvider();
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.allowedModels).toEqual(source.allowedModels);
+      expect(state.routing.allowedModels).not.toBe(source.allowedModels);
+    });
+
+    it("groupPriorities is a distinct object with equal values", () => {
+      const source = makeProvider();
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.groupPriorities).toEqual(source.groupPriorities);
+      expect(state.routing.groupPriorities).not.toBe(source.groupPriorities);
+    });
+
+    it("anthropicAdaptiveThinking is a distinct object with distinct models array", () => {
+      const source = makeProvider();
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.anthropicAdaptiveThinking).toEqual(source.anthropicAdaptiveThinking);
+      expect(state.routing.anthropicAdaptiveThinking).not.toBe(source.anthropicAdaptiveThinking);
+      expect(state.routing.anthropicAdaptiveThinking!.models).not.toBe(
+        source.anthropicAdaptiveThinking!.models
+      );
+    });
+
+    it("null anthropicAdaptiveThinking stays null", () => {
+      const source = makeProvider({ anthropicAdaptiveThinking: null });
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.anthropicAdaptiveThinking).toBeNull();
+    });
+
+    it("null modelRedirects falls back to empty object", () => {
+      const source = makeProvider({ modelRedirects: null });
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.modelRedirects).toEqual({});
+    });
+
+    it("null allowedModels falls back to empty array", () => {
+      const source = makeProvider({ allowedModels: null });
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.allowedModels).toEqual([]);
+    });
+
+    it("null groupPriorities falls back to empty object", () => {
+      const source = makeProvider({ groupPriorities: null });
+      const state = createInitialState("create", undefined, source);
+      expect(state.routing.groupPriorities).toEqual({});
+    });
+
+    it("name gets _Copy suffix", () => {
+      const source = makeProvider({ name: "MyProvider" });
+      const state = createInitialState("create", undefined, source);
+      expect(state.basic.name).toBe("MyProvider_Copy");
+    });
+
+    it("key is always empty", () => {
+      const source = makeProvider();
+      const state = createInitialState("create", undefined, source);
+      expect(state.basic.key).toBe("");
+    });
+  });
+
+  describe("edit mode", () => {
+    it("nested objects are isolated from source provider", () => {
+      const source = makeProvider();
+      const state = createInitialState("edit", source);
+      expect(state.routing.modelRedirects).toEqual(source.modelRedirects);
+      expect(state.routing.modelRedirects).not.toBe(source.modelRedirects);
+      expect(state.routing.allowedModels).not.toBe(source.allowedModels);
+      expect(state.routing.groupPriorities).not.toBe(source.groupPriorities);
+      expect(state.routing.anthropicAdaptiveThinking).not.toBe(source.anthropicAdaptiveThinking);
+    });
+  });
+
+  describe("create mode without clone source", () => {
+    it("nested objects use fresh defaults", () => {
+      const state = createInitialState("create");
+      expect(state.routing.modelRedirects).toEqual({});
+      expect(state.routing.allowedModels).toEqual([]);
+      expect(state.routing.groupPriorities).toEqual({});
+      expect(state.routing.anthropicAdaptiveThinking).toBeNull();
+    });
+  });
+});