Wims' case is an example of two commands in the same call chain: as the echo results show, fv1 in /filter's context is called before the second instance of fv1 in the editbox command. This is different from your /timer example.
I don't know if the current behaviour of $v1 (being available anywhere in the call sequence) was ever intended but it is now well known to scripters and I agree with Wims that it should work the same in /filter's context for the sake of consistency.
