Overlapping brushes in arena_nucleus (the first step of the stairs is sunk into the floor):
One bug that annoys me but is not related to mapping:
I'm sure you all know the feature to quickly switch between the two last used weapons (default key is Q) that is quite useful on the battlefield. By default this will switch between the first and second weapon slot or the third slot after you selected the melee weapon once. In addition to that you can go to Options -> Multiplayer and enable the option that your last used weapons will be remembered after respawning. No here's the bug related to those features:
As a Medic I prefer to use the Medigun/Kritzkrieg and the UberSaw for maps with cramped spaces so I select both weapons and can now switch with Q between them. However after respawning the Blutsauger in the first slot is selected and pressing Q will switch between that and the Medigun instead of switching between Medigun and UberSaw (....so remembering the weapons seems to be bugged). Also as the Sniper I have currently enabled the Razorback so the second weapon slot isn't available but pressing Q doesn't switch between the Sniper Rifle and the Kukri.