probably something like that. Because of zbrushes "hunt and peck" design with twitchy sliders located in same space you have to drag to scroll, it is really easy to do stuff like that.
So i checked, its only in that project. No matter what mesh i import into that project, the same behaviour stays. I opened a new ZBrush project and there everything is fine. So it must be a setting that i falsely set or smth like that? Anyway, i just imported everything in a new project and now works. Very weird. Thanks…