If the adjustments you're making involve draining the float bowls to gain access to the inner components, then the floats are probably just getting stuck in the down position because they're not used to going down all the way when there's fuel in the bowls.
If the adjustments don't involve draining the fuel, then the float valves sticking open is just happening by coincidence and you'll either need to replace the valves or clean them all really well, clean out the float bowls, clean out or replace the fuel lines, make sure there's no rust or debris sitting in the tank, and install an inline fuel filter.
Okay, so maybe that's a little bit of overkill, but you want to do the job right the first time, don't you?
In case of the first scenario, to help prevent this in the future, remove the float hinge pins and polish them up with either 00 steel wool or 800 grit sandpaper. This will help to keep the floats moving freely throughout their range of motion.
