Not currently able to reproduce this in XF 1.5, but either way, I don't believe this to be significantly problematic enough to consider fixing at this late stage in the life cycle of XF 1.5 and the issue is not reproducible in XF 2 either. There may be browser or OS differences at play here, but I suspect it's something internal to the editor so it may not be fixable anyway.
Let us know (via a new thread in the XF2 bugs forum) if it is reproducible there.