I think that is supposed to be a “feature”.
I’m willing to bet if you look in your “history list” for that textbox you will find the 0X0000 in it. I have noticed before that if a find or replace item starts the same as a previous one, ME wants to help you by filling the previous one in for you.
This is great if the thing you are entering is Longer than what ME is suggesting, you just keep typing and as soon as you type a letter different than the suggestion, the sugestion goes away and you are on your own again. This is also great if you actualy want the previously entered item in the text box, then just hit enter. If neither is the case I find you need to type extra characters(that disagree with the suggestion) then backspace to get rid of them.