While editing a question's tags, I noticed the following new, strange behavior:
Clicking on the (X) to delete a tag removes the tag, but immediately also follows the link to the tag page.
Typing a tag then selecting from the suggestions list with the mouse adds the tag, but also immediately follows the link to the tag page.
What makes this worse, is hitting browser-back from the tag page brings me back to the question, not in editing mode - all edits are lost.
Note: This seems to only happen on SO (i.e. it does not happen here).