Is there a workaround for the MonoDevelop collapsing bug?

Since Unity (finally!) upgraded MonoDevelop to version 4, a new very annoying bug has showed up: every time you save a file, the collapsing fails: everything is un-collapsed, and can’t be collapsed any more (the collapsing buttons disappear, and the collapsing keyboard commands just do nothing).

After a random while, it goes back to normal.
So far I’ve been unable to understand if there is one specific action that triggers it back to normal, or it really is totally random (though this seems very unlikely to me).

Is there a known workaround?

(closing a file and re-opening it doesn’t count)

There is.

As long as you both add any character and remove any character, the collapsing works again (preserving the bookmarks).

So after you save, you can hit the sequence: “space, backspace, undo, undo” (I’ve added the undo steps so that the file still counts as “unmodified”.