The information about browser version really helps to reproduce the issue on my local end.
I have submitted this issue to WebTextEditor development team as work item #1020. I will let you know any news I heard from the team regarding work item #1020.
I also would like to add something that I found during my attempt to reproduce the issue. The issue is not persisting when IE 9 is open in quirk mode. As a workaround, you might try to add following line into the <head> tag of your page in order to have the page open in quirk mode (by default).
<meta http-equiv="X-UA-Compatible" content="IE=5" />