In the editor insert five unique smilies in a row. They can be any smilies but for this purpose we'll call them A, B, C, D, & E. At the end of the last smilies press & hold the "shift" button and then press the left arrow button three times so that smilies C, D & E are selected. Let go of the shift button to stop selecting. Press your "delete" (or your "backspace") button to erase smilies C, D, & E.
At this point you would expect that what would be left on the screen is smilies A & B but, and here's the weird part, you instead are left with smilies A & C while B, D, & E are deleted. To show I am not cracking up, here's quick video capture.
XenForo Site: XenForo.com on May 7
Browser: Firefox 4.0.1
OS: Windows 7 Home Premium SP1
I also tried with Chrome 11.0.696.60 and do not get the same results.