This really has to be patched IMO. Many times have I wanted to pop a health capsule when suddenly a slime flies across the room due to charged attacks/bombs and hits me, or when I misjudge dodging distances due to lag (single bar connectivity for almost everyone not in the same country as the server, yay~). Then not only did I not gain any health from the health capsule, it counts as it being used up, so I have effectively wasted it. I can understand vials breaking when you get hit while holding them, but that's because you're HOLDING onto the vials. You don't HOLD health capsules when you use them - they are an instant use item.
To put it simply, if your health does not replenish, don't remove a health capsule from the belt.
Your getting hit...
If you use the health then instantly get hit, why would you have more health than when you started?