A tiny bug. Minor if you ask me, but might as well report it anyway :
If you open a document in the second editor using Alt-Click with the menu configured like this :
while having only one editor,
you end up with two editors displaying as if they were the only editor currently visible.
See how they both offer to be split, rather than to unsplit.
You have to click the split/unsplit button twice to revert to a single editor.
So far, it seems to be of no consequence other than that.
[EDIT] I just noticed it behaves the same when clicking a link that spawns the second editor.