The pantograph drop signs are beyond the platforms by around 2 coaches, and its an automated system, so all seems correct.
The instruction for drivers working passenger trains is to change to diesel mode when stationary and not wait until a few seconds after departure (as obviously the risk of distraction is greater when on the move), so it's not all correct as such, but again not a massive issue provided it is changed very shortly after departure. Test trains are permitted to operate with their pan up.
This all changes anyway on 30th December when electric passenger running through to Bristol Parkway commences.
There will be the following changes at Swindon then:
1) Trains to/from Bristol Parkway can stay in electric mode between Causeway and Bristol Parkway.
2) Trains to/from Chippenham or Kemble will need to change mode when stopped at Swindon station, unless not stopping at Swindon in which case:
2a) Up direction trains continue on diesel and perform a change to electric mode (at Didcot Parkway, if stopping there, or Moreton Cutting if not) unless their speed drops to less than 20mph when they can change on the move.
2b) Down direction trains must change back to diesel at either SW1161 or SW1163 signals.
At Bristol Parkway:
1) Down direction trains change to diesel where there will be signage just before the station, unless they are headed to Stoke Gifford in which case they can stay on electric mode
2) Up direction trains stopping at Bristol Parkway must change to electric mode whilst at the station.
3) Up direction trains not stopping at Bristol Parkway must change to electric mode in a special zone east of Parkway station.
Perhaps that little lot might explain why the odd mistake is made?