When you pick up a tab and ctrl+TAB before dropping it, the displayed file is the last one you TAB'd to and not the one you dropped. However, the file tab displayed is the one you dropped. In other words, the file tab and the code body do not match.
This isn't anything major, but it ended up causing me to save over a file I hadn't intended too. It wasn't anything holding down ctrl+Z for about 30 seconds couldn't fix but it was annoying none the less.