[TextField] variant="outlined" line through Label when used inside (first hidden) (eg. div) container

[cathiele]

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

When a TextField with variant="outlined" is child of a firstly hidden component (hidden=true) (e.g. div) and then displayed after the container is set to hidden=false, the Label of the TextField shows the line in the background of the label text

Expected Behavior 🤔

the line should not show up behind the label when the container with the TextField becomes visible

Steps to Reproduce 🕹

https://codesandbox.io/embed/material-ui-textfield-bug-qrgyc

import React, { useState } from "react";
import { Button, TextField } from "@material-ui/core";

function App() {
  const [formValues, setFormValues] = useState({
    text1: "text1",
    text2: "text2"
  });
  const [isTextField2Hidden, setTextField2Hidden] = useState(true);

  const handleChange = name => event => {
    setFormValues({ ...formValues, [name]: event.target.value });
  };

  const handleClick = event => {
    setTextField2Hidden(false);
  };

  return (
    <div>
      <Button onClick={handleClick}>show TextField</Button>
      <div>
        <TextField
          label="Text 1"
          value={formValues.text1}
          onChange={handleChange("text1")}
          margin="normal"
          variant="outlined"
        />
      </div>
      <div hidden={isTextField2Hidden}>
        <TextField
          label="Text 2"
          value={formValues.text2}
          onChange={handleChange("text2")}
          margin="normal"
          variant="outlined"
        />
      </div>
    </div>
  );
}

export default App;

Steps:

1. open the linked CodeSandbox
2. TextField1 should be rendered correctly
3. Click on "SHOW TEXTFIELD"
4. the rendered TextField shows line behind Label Text

Context 🔦

Your Environment 🌎

Tech	Version
Material-UI	v4.3.1
React	16.8.6
Browser	Chrome (macOS, Android), Safari (macOS

[oliviertassinari]

It's a duplicate of #14530