As others have already stated, this simply isn't true. I've owned both 5mm uncompressed and a 2.1mm compressed O'three neoprene suits - both of which were fitted with Apeks autodump valves on the left arm - and I never encountered a problem like the one you've described. To be honest, what has been suggested is impossible as the mounting ring that screws onto the back of the valve would have to be physically *unscrewed* by the expanding neoprene to have any effect on the valves operation. Even then, all that would happen is that your suit would flood! That's another myth busted, I'd say...
