mouse problem in fullscreen mode (slick2d)

Suddenly I have problems changing to fullscreen mode. My original displaymode is 1920*1080. I set my AppGameContainer to:

appgc.setDisplayMode(1280,720,false) and eveything works fine.

But if I set it to:

appgc.setDisplayMode(1280,720,true)

my screen scales and it looks good, but my mouse won’t go to the far right or bottom. I use Mouse.getX/Y() and when I’m at the point where it gets stuck it says 1280 and 720. Any ideas?