Thanks again. I thought I target UAE and such. But maybe I can improve speed again, as you pointed me to some clue.
The internal behaviour is, that any MOUSEMOVE is 'sent' to every gadget down the whole tree of objects, so that an object can change the pointer when the mouse is above it, or do something else then. Also, after each such message the whole tree is searched for gadgets that have been modified in order to refresh them. And while searching for such gadgets, any wanted clipping from their parent gadgets is applied. I don't know why switching the tabs is only "sometimes" slow. puzzling ...
If you have a good idea how to make this work in another way, I can change it. Now, here is a little testing program with which one can test a single class, if that class supports testing:
http://images.quicktunnels.net/oxtestclass ... usage is oxtestclass <classname> ... the classname is the name of the class file in libs:ox/ .. or the name of an internal class as displayed in oxlibinfo.