The door to Blackadder's study is open prior to Baldrick being thrown through it the second time. The camera pans to Blackadder, then back to the door, which is latched when Baldrick goes through it.
When Baldrick is showing the Bishop of Bath & Wells the painting of him in a dicey pose with Lord Percy, you can clearly see the unseen drawing is being held with the picture frame facing the camera, thus the Bishop is looking at the back of the painting.
After Edmund delivers the line "I only didn't laugh out loud because I was afraid if I did my head would have fallen off.", when the camera cuts back to Queenie the boom mic is visible at the top of the screen.
Blackadder says that gold is so-called because of its colour, when it's actually the other way round - the colour is named after the metal.