I think I've figured out the problem. Studiing the reactions of the keys. I came to this.
Sertain combinations of minimum 3 keys cause the keypad to block. The pattern is:

q---w-t---y
as-as-gh-gh

I think you could avvoid this by using the only keys from the same row or using only 2 key combination from different rows - like in CS:
W - walk foreward S- walk backward A- left D- right W+A - upper left, S+A backwards and left... As it is unusual to press A+W+S at the same time. Another thnig - this problem won't take place if you press key combinations from different columns like: A+F+O or Q+T+J...