If I paste the symbol "⌛" in a terminal, it gets very confused. For example, if I then pres "home" and hit space several times, the spaces will not appear and that symbol will not move. However after running the command, the command in the bash history will actually contain the spaces. Deleting the spaces will duplicate the symbol in their stead. Also, after pasting, selecting it, it looks like it's selected but normally something else is actually selected and goes in the selection buffer. I suppose other unicode symbols create the same issue.
This is because Qt mixes in different fonts, because your font does not have complete Unicode coverage. Different fonts might have different widths. *** This bug has been marked as a duplicate of bug 361547 ***