defineProps has invalid validation

[miroljub1995]

Vue version

3.5.16

Link to minimal reproduction

https://play.vuejs.org/#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

Steps to reproduce

Just open the repro link.

What is expected?

It should print no warnings in the console.

What is actually happening?

Typescript shows that C is union of string literals, but we get the error:

Invalid prop: type check failed for prop "c". Expected Object, got String with value "a1".
 at <Childc="a1">
 at <Repl>

System Info

System:
    OS: macOS 15.5
    CPU: (12) arm64 Apple M3 Pro
    Memory: 184.22 MB / 36.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.2.0 - /opt/homebrew/bin/node
    npm: 11.3.0 - /opt/homebrew/bin/npm
  Browsers:
    Chrome: 137.0.7151.104
    Safari: 18.5

Any additional comments?

Linked to this issue.

[jh-leong]

Closing as duplicate of #13444 since they share the same root cause. This regression was introduced in 3.5.15 (3.5.14 works fine).