Why is my keyboard being wierd?

I play World Of Warcraft, and when I’m running using the WASD keys, the arrow keys or the numerical keypad the same problem happens. when I’m running with the forward key and then choose to change direction by strafing (Q, E, ^, >) once I let go of the new direction key I stop moving, this also happens when I hit space. I am using a PS2/USB Adapter and before I got it this was not an issue, I looked throught the keyboard / windows access options and saw nothng that would cause this. I’m currently running Windows Vista. Any ideas?

I have not tried testing this in any other game.
And this is not a Sticky Keys issue. :)