v-model on <select multiple> uses stale collection type after switching between Array and Set

[zongxi1115]

Vue version

3.5.39

Link to minimal reproduction

https://play.vuejs.org/#__PROD__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

Steps to reproduce

1. Bind a <select multiple v-model> to an Array.
2. Switch the bound value to a Set at runtime.
3. Interact with the select again.
4. The emitted model becomes an Array again.
5. Switching back from Set -> Array shows the same stale-type behavior in reverse.

What is expected?

The current collection type should be respected after the model switches at runtime.

What is actually happening?

The change handler keeps using the collection type captured when the directive was created, so the first user interaction after a runtime Array/Set switch emits the old type.

System Info

Any additional comments?

No response

[barry166]

From vModelSelect.created, isSetModel is captured once from the initial binding value and then reused by the change listener. A tiny regression test could mount with an Array, update the model to a Set, trigger change, and assert the emitted value is still a Set; that should fail before moving the type check into the listener.

[zongxi1115]

Thank @barry166 ! The added regression test follows this path, it mounts with an Array, updates the model to a Set, triggers change, and asserts the value remains a Set.
I also kept a small follow-up assertion for switching back to Array, but the main failing regression case is the Array -> Set path you described.