I have just downloaded and started playing with GPO4, and I find a strange bug when using it with my DAW (Digital Performer 6.02). The behaviour started immediately upon starting to use GPO4 and, so far, has only occurred when using GPO4 as a plug-in with DP6, so it seems to me that there is some incompatibility there.
Here's what happens: the DP6 Project>Add Track menu loses its submenus.
This happens fairly frequently, but not all the time, which is just as well because that would make the combination unusable.
When it happens, I can get back to normal by simply quitting and relaunching DP6, so that's my current workaround.