I think I have noticed a bug with Backdraft:-
When you have backdraft and you cast and instant cast it does not reduce the number of charges which seems to be the way the spell works.
However if Nightfall procs at the same time (the Glyphed version) that makes your shadow bolt instant it seems to consume a charge. I think I came accross this last night but forgot to test it further.
Anyone else had this - Surely instant casts shouldn't consume a backdraft charge ?