OK, here's a simple one to start with. This was something that I saw happen to a buddy, rather than myself (I'll post some of my own screwups later
). Some aspects of the incident have been discussed on here before (
Missed stops protocols? ) but I'll post it again in the interest of getting things started.
My buddy (not on YD) and myself were ascending from a 35m dive. At around 20m he lost control of his buoyancy and shot to the surface (he was fortunately unharmed).
The cause of the incident was accidental inflation of the redundant bladder in a twin-bladder wing.
He was diving with the second inflator attached, routed under his arm I believe. At some point the inflator became wedged between his arm and body (probably as his arm was in 'holding the reel' position), the inflator button was pressed and some gas was added to the spare bladder.
He did not realise this, and spent the short trip to the surface desperately trying to dump gas from his suit and main bladder, not knowing it was the spare bladder that was the problem.
Lesson learned: if you dive with a twin bladder wing, it may not be a good idea to have the second inflator connected all the time. He normally did not, but had been wetsuit diving on holiday with it, and had simply forgotten to disconnect it.