Hi David,

Many screens stay on in a car until the car is locked and even then for a few seconds. Have you checked if it stays on for long after you've left the car and locked it etc? 

We've not heard of any common problem with this in the Insignia, so if you think it really is a fault then it'll need to be looked at by an auto-electrician or a good mechanic. An Opel dealer would be the best place to start as it could be something they are familiar with.