Traffic light confusion

The traffic lights at the roundabout on Tewkesbury Road where it meets Princess Elizabeth Way are causing confusion. Traffic going round the roundabout from Tewkesbury Rd into PEW often go through the lights when traffic exiting Cheltenham have a green signal. Equally traffic going straight on out of Cheltenham often go through the lights when traffic going round the roundabout have a green signal. I have inadvertently made both of these mistakes at different times, and have now seen other motors making those same mistakes. I'm not sure if this is because the traffic light post has been slightly rotated or the louvres on the traffic lights are ineffective but it is a serious situation just waiting for accidents to happen.