The following bug is 100% reproducible for me:
- write a multi-line post (either new or reply).
- go back and do any kind of formatting on a line that isn't the last.
- the formatting correctly affects the selected text.
- the formatting doesn't affect the following line.
- the formatting incorrectly affects all of the text from the 2nd line down to the end of the post.
- do some more formatting. sometimes it affects the other lines, sometimes it doesn't.
- edit a later line. sometimes the incorrect formatting goes away.