Left and right movement not equal speed

Newbie & Debugging Questions
#1

Hi,

I noticed a huge “bug” in my Game.
The left and right movement are not equal in speed:

going stair up


activeProt.x += 0.5f * delta;
activeProt.y -= 0.5f * delta;

going stair down


activeProt.x -= 0.5f * delta;
activeProt.y += 0.5f * delta;

When I go down, the character won’t go through the starting point. It goes more to the right.

I already noticed, that going straight left and right are at a different speed. Right appears do be faster. Why??

I set the FPSTarget to 60.
By the way, I am using Slick2D.

Thanks for your help.

edit:

the x and y coords are integers… is that the point??