besides jitter (mainly Qt stuff) i also had trouble using
big bpatchers and the waveform~ object on windows.
the most important thing you should not forget when building
on mac for windows is to make proper names for abstractions and subpatchers which are compatibl with the windows converntions
for filenames, and, of course, make sure third party externals
you use are available for the other platform.
problems releated to midi and audio IO ponly appear the
first time, later you know what to do.
the most annoying thing for me is that on windows Max 5 uses the MDI (Multiple document interface i think). This means that if you alt-tab you potentially have what appears as lots of different max applications running (one for each patcher window). If you have a vst plugin loaded that has it’s own entry on the alt-tab menu (what other application does that????). This behaviour is obviously the same for standalone apps.
Personally i never saw any problem with how windowing worked in Max4.