When i registered i was not able to log in, so i recovered the Password.
Then log in worked.
But when i try to change my Password I can not type more than 8 characters and it doesn't save the new password. Instead I have to use the Password I got by E-Mail when i recovered it.
How can I change it?
Is there a limit of 8 characters?

There is no password limit, I would check removed any saved passwords for this site in your browser's settings. That most likely is what is populating the password field.