Spellthief Inconsistencies (Bug?)

Why is it that Brand's passive procs Spellthief multiple times, but Morgana W can't?

It doesn't seem right that something like that is gated on one champ, a change designed to prevent them from stacking it too fast, but then allowed on another one, who can stack it at the same speed (if not faster).

All Brand has to do is hit one W in lane, and he'll get all 3 of his ticks. Meanwhile, Morgana has to W, hope both champions walk into it, then get an auto off on one of those two champions to get all 3 ticks.

Why does Brand get to be safer for the same end result? There needs to be some parity on the proccing of Spellthief's. Either make it so that all DoTs can proc it multiple times per cast (which will put Morgana W right back where it was before the change), or remove the ability for Brand's passive DoT to proc Spellthief's multiple times.