Like what's been said above, I run into this bug most often when pasting from other places (though I can't confirm that's the ONLY time it happens).
One trick I've found is to make sure the text being pasted in is in plain text format, not in HTML format. That's a little tricky, because you can't always SEE that it's html. (If I'm struggling with an existing note, I just copy all the content out of the note, into an external program, and then back into the note.)
I typically paste the text into a program like Notepad++, then immediately copy the exact same text out of Notepad++ and paste it into PT. When you copy out of Notepad++, it's only putting the text information in the clipboard, not any html information.
Actually, I often just paste it into our back translation in PT, then copy it out of there and paste it into the flag (the BT works like Notepad++, only retaining the text and not the html formatting). Then, I usually remember to delete the temporary text out of the BT. 