You know you can build deck off a joint and then delete the deck portion, so that the crossbeam disappears? I find it a very useful "shortcut". (but of course, I'm too lazy to change planes and delete it manually =P)
Well, the bug is this: Building deck off a joint then clicking undo deletes the deck, but doesn't replace the z-beam.
Like I said, nothing more than a minor annoyance, but I wanted to sound important by submitting a bug report! So please cheer for me and send money to (censored)