I'm getting weird and hard to reproduce issues when attempting to extend/override a type's merge function.

I ran into this a while back when extending coercedTo into a deprecation transition type.

I just ran into it again when attempting to remove a deprecated attr from a submodule's final value.

I've attempted to find a MRE, but in simple examples overriding the type's merge attr seems to behave as expected.

Have I found a nix bug? Or is there some other quirkiness going on here?