Spell prevention is not triggering on spell interrupt

[Cromisa]

Basically any ability that interrupts a spell and "prevents any spell in that school of magic being cast for X seconds" doesn't work. E.G Earth Shock for Shaman, Shield Bash for warrior, CounterSpell for Mage etc.

The interrupt works correctly, but the mob straight away begins to cast the same spell again.
Silence effects work fine, but they stop all spells, where as the ones mentioned above should prevent a certain school of magic for a duration.

To Reproduce:

1. Find a spell caster mob while playing a Shaman
2. Interrupt their spell with Earth Shock
3. See that they cast the same spell right away