Blackadder salutes General Melchett without his cap on. He should have only stood to attention instead.
Lord Flashheart's rank would not have been Squadron Commander, as that was a rank in the Royal Naval Air Service, and Flashheart was in the Royal Flying Corps. Depending on the length of service, the equivalent RFC rank would either be a Captain (fewer than eight years' seniority) or a Major (more than eight years' seniority.
Blackadder asks for a message to be sent to the Head of the Royal Flying Corps, Air Chief Marshal Sir Hugh Massingbird-Massingbird VC DFC and Bar. Air Chief Marshal is a rank of the Royal Air Force, and was not instituted until 1919, two years after the episode is set.
During the end scene, Captain Darling is backing to the table with Flasheart standing atop of it. Rik Mayall bends his left knee out to signal Tim McInnerny to stop.
When Lord Flasheart punches Blackadder, he hits him with his left hand, however, Blackadder tilts his head and falls as if punched from the right.
A wall wobbles when Baldrick falls against it after being hit by Lieutenant von Gerhardt. This happens again when Baron von Richthoven hits him.
On landing in Blackadder's trench, Lord Flashheart wrongly concludes he has landed in a German trench. It is nonsensical that he would make such a conclusion since Blackadder was wearing his British Army uniform at the time and Flashheart should have known from this as soon as he saw him.