jdf:
It seems that the inflator hose does not have a flap or diaphram to keep water from going inside when you pull on it to deflate it.
I've never seen one that does have a flapper or valve. If it would keep water out, how would you get air in? (when youinflate your BC, it follows the same direction/path as water would enter) What were you diving previously? As the previous poster mentioned, if you hold the exhaust valve open after the air has all been expelled, water can and will enter the bladder. Some BC's are more positive than others, so you may have been a bit overweight before and now correct or spot on before and half a pound light now, which will leave you trying to exhaust air that isn't. Also some valves will exhaust air faster than others (if you're in an undesired ascent, maybe the inflater valve stuck, fast is GOOD). On "better" BC's you can exhaust air faster than the inflator can add it. Becuase there's a larger air passage, it's easier to get water in there too.
If it's fresh water, manually inflate the BC, turn it over and get as much water out as you can, then fully inflate to store (if you're travelling do inflate it and let sit that way as soon as you can). It may take a couple of cycles, but the moisture will evaporate inot the air in the BC and changing the air, will eventually dry it. If it's salt water, drain, flush with fresh water. Even with fresh, it's not a bad idea to flush the interior now and then. I usually do it by removing the rear dump, ouring a good bit of fresh water in, put the dump valve on, inflate and 'shake it all about', then follow the drain and dry method above.