The "Sticky Keys" shortcut is activated by hitting the Shift key on your keyboard or button 4 on the X-Arcade 5 times.
To disable it:
Hit the Shift key 5 times to activate the StickyKeys shortcut (if it does not come up, then you do not need to continue).
Click the "Settings" button or "Go to Ease of Access..." link.
On the next window that appears (click the first "Settings" button again if there is one) under StickyKeys remove the checkmark next to "Use Shortcut" or "Turn on Sticky Keys when SHIFT is pressed five times".
Click the "Ok" buttons to get out of these windows, and it should no longer bother your gameplay.