Key sequences erases typed text

[Magnum]

Sometimes when I am typing text in a text box in my browser, I will lose all of my text.

This usually happens when I am close to finishing.  :P

It may be some key combination using keys in the Left Shift,Ctrl, and Windows key area.

I just found the undo function, but would like to know how to prevent it from happening in the first place.

Any ideas ?