In CKEditor, Pressing Enter Acts Like Page Down

When I edit a campaign document, using CK Editor, every time I press Enter, the screen scrolls up as if I pressed the Page Down key. Curiously, actually pressing the page down key does nothing.
It does the same thing when I press Ctrl-Enter too.
As you can imagine, it gets pretty annoying since the enter key is used quite often.

Thanks for any help,