The Armoured Might of Lance Corporal Jones - S3-E1
Corrected entry: Cpl. jones has converted his butcher's van into a troop carrier. It has concealed holes in either side and in the roof to shoot the platoon's rifles out of. When the platoon show Cpt. Mainwaring their drill, the command is for five rounds to be fired out the lefthand side, then the righthand side, then the roof. But instead of firing out of the lefthand side of the van, the platoon fire out of the righthand side twice.
The Armoured Might of Lance Corporal Jones - S3-E1
Corrected entry: In the episode 'The Armoured Might of Lance Corporal Jones', Mainwaring has Jones' van converted to gas. However, for the rest of the run of the programme, the gas bag has vanished, and the van runs on petrol.
Correction: The gas bag experiment was a total failure, and almost all of the conversions were promptly converted back. This is exactly what happened to Jones' van.
Correction: Yhe Warmington-on-Sea platoon are not the sharpest, most efficient military squad and it is quite likely the orders were botched. Regardless, at best it is a character choice and not an actual mistake.