Pirates have a boosted mp gain formula.

Pirate
*HP/level: 22-26 +(Improving Max HP Increase)
*MP/level: 18-22 +(Total INT/10)

*HP/AP: 18-22 +(Improving Max HP Increase)
*MP/AP: 14-16

*1st job advance HP: 100-150
*1st job advance MP: 25-50
*Minimum HP: Level*22+80
*Minimum MP: Level*18-39

*2nd job advance HP: 300-350
*2nd job advance MP: 150-200
*Minimum HP: Level*22+380
*Minimum MP: Level*18+111

This is all from the Your Guide to HP and MP thread by LazyBui. And uhh... it's been there for a while.