Samsung SGH-Z510 Keypad

I've recently started using a Samsung SGH-Z510 and am beginning to get
annoyed with the keypad. It seems that however hard I try, it almost
always double clicks on any of the buttons when I just press them once.
Sometimes it behaves, but mostly not. It seems like the sensitivity
of the buttons is set too low or something.

Has anyone else experienced this problem, or found any cures?

Do you have a cover on your phone? This was a problem for me but without a cover it's fine.