Never run into this but I have read about it. I copied a single comment from youtube, pasted it into Notepad and 7 of 8 lines (wrap is turned on) pasted fine - default Lucida Console 12 point. But one line in the middle is about point size 8 or 9 and a different font, not sure which.
If I select all the text and change to a different font, everything is uniform. If I go back to default, the problem returns. If I try to save it in the default settings, it says I can't because that one line is in Unicode and the rest is ANSI. (It saves anyway.) I tried copying and pasting from comments in other videos and the problem occurs. Even if it's just one line, that line gets messed up.
In the grand scheme of things this is pointless. But what gives?
Problem Completely Deleting Notepad++ 
