Lesson learnt there I think, car hasn't done it since, but the micro switch playing up is definitely a possibility.
I now know that the TF will auto lock if the car is unlocked with the fob and the doors are not opened, (keys in pocket) although it takes a minute or two. Didn't know the F would do it with the keys in the ignition though.
Cars are safe enough as they are parked up at the back of my long drive behind two Volvos, just a bugger to move around when I get the chance to take one for a drive