Found a bug that I've been aware of for some time, but have been unable to pin it down...

If you 'edit' a post, replacing test with something different, and the add a mark-up to the text, such as making it bold, the old text that was replaced reappears.
Seems to cause different issue if you select just the new text to mark-up, or include some of the original text.
I've seen something similar when adding URL links to text too.

Hope that help.

Steve

I sometimes notice a similar behavior, but thought it was Firefox issue, hard for me to recreate. I thought adding selektion=""; would fix it but it still appears.