All my tests (on my gm with 100% proc weapons, on my gm duel wielding proc weapons, a random player with my 100% proc weapons, said player with his own proc weapons, my GM casting with a BP that procs every hit) all proced while in mid cast/sing.
I had totally forgotten about innate procs, and didn't test them. Haven't gotten around to fixing them yet, but they are on my list.
Not while singing songs it doesn't.
Issue confirmed. Looking into whether we want to change this though.