I've see this a couple of times today in ST2. If I copy a line without selecting anything and hitting Ctrl+C. I then place a few cursors in other parts of the file and hit Ctrl+V.
The first cursor correctly inserts the new line, but subsequent cursors insert the new line and, on the line following, one or more NUL characters appear. The behaviour is sporadic and not easy to replicate.
Anyone seen this?