This is one of the Keystone changes we'll be trying out in the Beta soon:
Edit: I suppose I should note this character has Eldritch Battery. Her Energy Shield is now paid before mana.
Edit edit: All the usual effects on Energy Shield will still apply to this ES - Recovery delay, Ghost Reaver, Zealot's Oath, etc. You'll not have any more base mana than you would have had prior to taking the keystone, though. Damage won't interrupt ES recovery any more, only losing mana or ES will.
Edit edit edit: Stun avoidance will no longer apply. Arctic Armour will still drain mana, ignoring Energy Shield,
as will Mind over Matter. You can't reserve energy shield, so you'll just reserve the mana underneath.
Edit by Mark: Mind over Matter doesn't take from mana like AA, it damages it, which would be protected by ES in this case, since damage is what ES protects from.
More background: This change has an interesting history; I suggested it offhand as a strange idea, but it solved a few key factors we were investigating, like AA/MoM defense being too high for too low a cost, so it was decided to go ahead and try it out. It's quite likely we'll see other changes to the kesytone as testing progresses, but because it's such a big change to one of the most popular Kesytones, any sweeping change won't be made without testing the waters carefully. The change isn't intended to 'kill' any mechanics, but will give us the opportunity to reassess some. Edit: Like the mana drain amount or mechanic on Arctic Armour
Edit: Thanks for your thoughts, everyone! The team will definitely be discussing it on Monday, and we'll keep you abreast of changes as they're made. Keep your concerns and suggestions coming.