tested this by making a module and receiving that packet every time a skill was used//the char attacked, here it is if you want it:
http://gamers2k4.com/starfish/pics/mana.zip
(changed link, it's TrinT's module which is better, compiled it for you)
my mana "jumped" up to 52 even though I only had 11, but in the same instant it jumped back to 0 as soon as I used BO (costs 11 mana) ... dunno, needs more testing I guess