Ok 4 all who have same problems or are interested in why on many keyboards only 2 keystates can be read:
It is a feature in the hardware. It depends on the keyboards hardware how many pressed keys are recognized. Older keyboards support many keys pressed. In the latest development however (especially on the Laptopsector) only two keypressed are recognized.
There are still keyboards that recognize more ... but do you want to let your customers let buy new keyboards? I don't
Can anybody confirm this? Or found a way to enable more keys?