Hi Rob,
This is another materialization of the main problem with the Cocoa PI Mac OS X version: mouse events not being received correctly by the corresponding controls. The same problem causes most of the cursor drawing problems on image windows; for example, mouse enter and leave events are simply not delivered *sometimes*. This is IMO a Qt bug, which I unfortunately have no time to document properly (it requires writing a test application that reproduces the problem, which doesn't happen in trivial applications). It could be also something I'm doing that doesn't work on Mac OS X, but ... the same *exact* code works without flaws on Windows, Linux, FreeBSD and 32-bit (Carbon-based) Mac OS X.
Fixing these problems is a hard and extremely time-consuming task, which I'll face as soon as I can deliver a reasonable amount of new documentation, another version of PI Core to fix known bugs and provide essential PJSR and GUI functionality, and stabilize other important things in our company... so please be (even more) patient.