There is the physical and mental aspect of this. The information I received (assuming I understood it correctly) is that the difficulty in exhaling is less than inhaling.For clarity - I'll say there was no medical diagnosis - it was always assumed that what happened. I think you're right about the being able to exhale - since I'd tried to purge the second reg - I don't recall any resistance to the exhale. All I vividly remember is not being able to inhale - and I'll never forget that feeling of my chest heaving in and out with nothing in my lungs.
THe point I really was trying to convey, that your brain's self preservation instinct kicks in. In my case certainly, but I suspect everyone else too, there's no conscious thought about lung over expansion - you know if you don't get to the surface you're going to drown. But rational thought doesn't happen, it's all instinctive reaction.
That said, there is the psychological aspect of how an individual may react in which they realize that there is something wrong with them and not their equipment. Not being able to breath is likely to be fear inducing. What the individual does in their flight is critical to their survival. I do not wish to hypothesize further as I am unqualified to do so.
I’m still mulling over how to present the information gleaned from this thread.