Type this command, and see if the box keeps occurring:
/remote off
If that solves the problem, then you have a script loaded that has a onINPUT event within it. That event is adding your mystery character. Your friend should be able to copy that character by selecting at least one other character at the same time. For example, in your image, he should copy []H and then paste that into this command:
//echo -a $asc([]H)
and then delete only the extra character
//echo -a $asc([])
Note: that box may not show up visibly in your edit box, but it should still be there.
-genius_at_work
