This about what happens when two stacks of Tempest are active for each of the Stormbringer specs:
Enhancement: After Primordial Wave, the next Lightning Bolt uses both charges of Tempest and hit with the first one 100% enhanced by Maelstrom weapon stacks and with the second one for 175% enhanced by the same Maelstrom weapon stacks and number of Flame Shocks.
Elemental: If the mastery procs for the first Tempest, it will consume the second charge. This way the second Tempest charge will be consumed by a Mastery Overload Tempest that will deal 35% (with Echo Chamber) of the original.
So, stacking Tempest meas that Enhancement deals 275% Tempest damage enhanced by Maelstrom Weapon stacks and number of active Flame Shocks, while Elemental deals 135% Tempest damage.
Conclusion:
As far as I’ve seen, fixing the Elemental bug will make Enhancement not be able to dischange two Tempests at once.
I have no idea how this happens after months of Alpha testing and months of Beta testing.
I noticed this immediately after switching from Enhancement to Elemental.
If this gets fixed somehow, please don’t just cut the damage of Enhancement to put it in line with Elemental.