Key does not turn after replacing petrol cap

I stopped for petrol, replaced the petrol cap and then tried to start car, but the key only turned halfway in the ignition and the indicator lights both flashed, but the key would not turn all the way. I tried removing and replacing the petrol cap again (using the key) and this time the key turned in the ignition and the car started fine. I was wondering if it was actually something to do with the petrol cap, and there being some automatic system where you cannot start the car if the cap is replaced incorrectly. Or might there be some other reason for this?