Hi, Jules. We just found an easily reproducible bug in the JUCE svn tip (or at least as far as revision 684).
Start up jucedemo.app.
Focus another application such as Finder.
Right-click on jucedemo icon in dock and select quit.
jucedemo.app doesn’t quit until it receives focus again.
EDIT: Forgot to mention, this is on 10.5.