I've noticed that when spamming Burst Fire (gunslinger triple shot) against a target or not, my MP goes up by about 300 every 10 seconds. I have no MP pots being used, nor do I have auto MP (only auto HP). Attached video: I don't have any other PS installed, and I believe the issue was happening yesterday as well since I didn't buy any MP pots after training. Edit: Might have something to do with the key? I use Shift for it, and when I hold Shift on a ladder, my MP regens about 50 instead of 10. Very weird.
Can confirm that each cast of burst fire increases my next natural mp recovery by 22. (10 naturally, 1 burst fire = 32, 2 burst fire = 54, 3 burst fire = 76). If you stopped casting after buffed mp recovery, the mp recovery resets back to 10mp. The mp cost of maxed burst fire is 22, you essentially recover all the mp you used back on your next natural mp recovery. Occurs on B key or shift key, did not try other keys. Edit: It appears that it's not related to mp recovery. You heal (22*#ofBurstFireCasted)mp after your next change to your current mp (except change in mp because of burst fire), whether it's your natural mp recovery or mp consumption from casting other skills.