Yep or close the window with the app before re-launching the debug session also works as well.
FB on OSX has a lot of drawbacks - on win, the help gets its own window (so it doesn't get killed by the debugging), syntax colouring works better, images actually appear in design mode all the time, it builds a lot faster (iMac in BC spanks my mac pro in OSX), the text editor doesn't lag when doing fundamental things like selecting text. Oh and I love it when FB seems to get confused and tries to launch a debug session but in reality it's just sitting there and waiting to time out. At least embedded fonts still disappear on both platforms in between compiles for no apparent reason so I don't feel completely screwed over. If it was edge case stuff, it wouldn't be a problem, but this is stuff you have to put up with every couple of minutes. Nik

