Thanks for the info Foxtrot.
I'm not sure if any of this has to do with you being on a Mac or not. To be honest, I'd got to the stage where I was willing to just drop even pretending to get cross-platform compatability sorted. This was due to me making extensive use of SwingWorkers which I believe aren't supported by earlier versions of the Mac JVM. Are you using the last version I posted? I need to check it out and see if I had implemented any workers in that version because if I did, this at least gives me hope that it can still work on newer OS's.
As for the problems... I think I recognise the second one you mention, where generate doesn't seem to refresh it. I vaguely recall having a bug where I had somehow broken generate under certain conditions. If it is that bug, then it should be possible to refresh your parameter changes by either using the "apply" button at the bottom, or by using a command such as "apply spaces" or something and then turning it off again.
I would have put the first problem down as a memory problem if not for the fact that it happens when using a brushset with more than one brush. This shouldn't really have an effect on memory usage. I'm at a bit of a loss really.
I'll have to try and find some time soon to get a new version uploaded. It may be that I've already solved all your personal problems with it as I did spend quite a bit of time on it after that last update. I'll try to tie up some loose ends on it and get a new version posted soon.