I'm not sure if this is a bug but....
One of the throwables is called "Lesser Abjurative Powder". I think it is just supposed to be svirfneblin disruptor but the name is confusing and prevents stacking with disruptors.
Not a bug. The reason they do not stack I think is because they are of different dispel strengths.
Well I'm pretty sure the inventory acquisition message is "disruptor" but when you look in your inventory it says lesser abjurative powder