Interesting. I stand corrected then!
You could also perhaps guage it by the amount of ammo used. A fully charged shot should use more ammo than a regular shot (though you don't "lose" the charged ammo until you actually release the shot).
I would assume the hosts' invisible bar would retain the same properties, but then it's even harder to guage if you have a shot "ready to go."
That too could be a bug. Anyway, this is something they need to patch. It's just that people who never host non-dedicated won't notice it.