There are some quirky things about DH regs. One thing that had me scratching my head for the longest time was that periodically, I would get a little water in my mouth when I breathed in using my Royal Aquamaster. I spent the longest time looking for leaks, plugging things up, submerging the reg, inhaling and trying to figure out how the water was getting in the cans. Everything seemed tight, so I couldn't figure out how it was happening.
Then one day it happened when I was diving and the answer just dawned on me. I had let it free flow for a few seconds during my surface swim. While it was free flowing, water had the chance to seep in through the open wagon wheel valve and had flowed down the hose and into the can. Later when I was angled downward and to the right that water flowed back out of the can. There was nothing wrong with the reg at all. I just didn't understand some of it's characteristics.
Other things that stand out about double hose regs are the differences in breathing effort based on your body position. Probably the hardest positions to breathe in with a double hose are horizontal either facing up or down. Facing down, it's harder to inhale. Facing up, the air is pushed into your lungs, and exhaling is work. If you're ever tired and laboring to breathe, rolling to your side, (doesn't matter which one), makes things significantly easier.
The other thing that you really need to learn with a double hose is how to clear it. Fortunately, it's very easy. Simply roll to your left side and raise the mouthpiece until it starts to free flow.