Spells: Regrowth Stacking

[Daldaen]

So I had this issue happen to me late last night and I didn't think much of it til it happened twice more this afternoon.

Basically the situation is I'm under Stinging Swarms DoT from mermaids in Kedge Keep. My Regrowth drops naturally (fading due to duration). When it fades I try to reapply Regrowth, and it won't stick because the Stinging Swarm DoT is still on me. This isn't how it is supposed to work...

Regen effects aren't blocked by DoT effects, atleast they shouldn't be. Screenshots:
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(Me starting to cast Regrowth as seen in bottom left catch window)
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(The spell 'landing' and saying the lore text of - You begin to regenerate - but clearly not landing, and wasting 300 of my manaz!)