this is the problem:

happens with every color

these are my settings:

when i turn gobos off, the problem is gone, (even though these fixtures are rgb pars) and when i check opengl compatibilitymode, the problem is also gone, but i believe that's the old 3dview.
the problem does not occur when using moving heads on open, but when i use a gobo with gobos enabled in the settings, the problem does occur.