Svelte 5: bind:group incorrectly considers other groups when changing value

[ciscoheat]

Describe the bug

When using bind:group on a store with nested data, previous groups are taken into account, returning an incorrect value when updating the store. This worked fine in Svelte 4.

I tracked the error to the functions bind_group and get_binding_group_value in render.js, where it seems like all groups are concatenated into one, which will be used in the latter function.

Reproduction

Svelte 5 preview site

1. Uncheck "Mint choc chip" checkbox
2. Current flavours will change to "1" (expected an empty array)
3. Check it again, Mint choc chip will be added after the 1

Logs

No response

System Info

Svelte 5 preview site.

Severity

blocking an upgrade

[ciscoheat]

Any news on this? It's basically what stops Superforms from working in Svelte 5, so it would be great it it was fixed.