JVC Everio GZ-MS90E aspect ratio is 5:4 instead of 16:9
Now I found the right way for my footage. It was simple: Just right click on the footage, and select Ändern » Filmmaterial interpretieren. This is probably Change » Footage or something like that.

Then I fored premiere to use the aspect ratio D1/DV PAL Widescreen 16:9 and everything is fine.