luckily I could solve the problem. I don't know exactly why it's working now but here is what I did:
Installing EQMod, Stellarium_Scope and Stellarium on a windows pc. Configuring the mount. I got the same problems. But here, the reverse DEC, reverse RA switches worked so I found out, that the DEC axe slew wrong.
Reconfigured my mount controller to reverse DEC (in fact an d in my case RA is reversed, DEC not).
I took me a long way here. I estimate because initially a already tried to reverse DEC i can only assume, that either I missed something or the windows setup trigged something in the mount controller so everything is working know. Glad it's no bug.