Leaving it in the sun is what his disfunction is. Put a spare shirt or towel over your markers when you are not playing to solve 95% of his problems.
What is happening most likely is that liquid CO2 is creeping into the hose and expanding in the heat from the sun. That is, unless you are in an area that isn't warm recently? Azodin also isn't known for their quality, so it could also be that.