It happened in V5. In Windows.
AFAIK, it's all to do with the fact that Poser (the core of it ,that is) was written to be be "cross-platform" (PC & MAC).

The 2 systems use different "communication" methods regarding user interface.
On the PC, when you open up a menu, Poser seems to do all the usual things (as expected by a Windows user),  but interprets some of the messages differently. Windows doesn't realise this, and also interprets those mouse clicks. So Windows shifts context, and tells Poser that the context has changed...

I could give some specific examples/reasonings, but I've learned to sigh live with it and so I won't

Cheers,
Diolma
(Who is too tired to get into a long discussion tonight - maybe tomorrow)