Issue with Fade and Transition when passing timeout.exit as undefined

Steps to reproduce

Steps:

1. Open this link to live example: (https://codesandbox.io/p/devbox/customizedinputs-material-demo-mui-7-forked-96ppx4?workspaceId=ws_UJkQicAXB81GxgEvK1MtbZ)
2. When providing slotProps.transition.timeout = {enter: 1000, exit:undefined} (which is valid according to the types)
3. When the transition unmounts, the transition state never makes it to 'exited' (as shown in the demo)
4. The 'transitioned' component stays on top and prevents interacting with things that were underneath.

Current behavior

3. When the transition unmounts, the transition state never makes it to 'exited' (as shown in the demo)
4. The 'transitioned' component stays on top and prevents interacting with things that were underneath.

Expected behavior

The visibility prop is set on the node correctly and allows interacting with things that were covered.

Context

Some of our users have raised that this same effect is happening with Modals closing, which is causing us major headaches. Whilst I've witnessed it with my own eyes, there's no timeout.exit = undefined setting in our codebase that I can find.

Any insight to what might cause the exact same behaviour, but with modals closing would be extremely valuable to me.

Your environment

  Don't forget to mention which browser you used.
  Output from `npx @mui/envinfo` goes here.

Search keywords: Fade Transition timeout.exit as undefined

Start with the linked CodeSandbox reproduction and inspect the Fade/Transition handling for slotProps.transition.timeout when exit is undefined. Compare the unmount path with the reported modal-closing behavior. Done means the transition reaches exited, sets visibility correctly, and no longer blocks interaction with underlying content.