I may be misreading the problem you're having, but have you checked that it's not the secondary editbox for channel windows (ALT+Q). You may have accidently bumped it at some stage, the check box to turn it on isn't in the Options dialog that I know of, so looking for it there won't help. You have to either right click on the editbox for channel windows and goto 'Options' or open the menu for the channel (right click on the switchbar button) and click on 'Editbox'.
