I have an Apple wireless keyboard and mouse. Whenever I hit the shift bar when I'm typing, the symbol for the shift key pops up in the upper right corner of my screen. If I hit shift twice, the shift key locks down and capitalizes everything. This is also true for the Control, Option, and Command keys. How do I turn this off? It's very irritating, especially with the sound it makes everytime I hit one of those keys. Thanks for your help!