My guess is since that the upper level masteries (I think it's mastery 7 and beyond) don't have quest SP, you can use their SP in lower level masteries if you want. But masteries 1-6 have quest SP so they disable using their SP in previous masteries. Just guessing though.
Edit: It appears that Evans can max all of their skills, at least according to this video of a level 137 Evan at Skeles. Are there SP quests for all masteries since he has every skill maxed (except his current mastery, obviously). :f6:
http://www.insoya.com/bbs/zboard.php?id=...sc&no=8117
Another thing I noticed is the description on Amp in the video says +120% damage, not +135% damage, unless that's just a typo like Fiel said (plzplz be a typo).
Edit: It appears that Evans can max all of their skills, at least according to this video of a level 137 Evan at Skeles. Are there SP quests for all masteries since he has every skill maxed (except his current mastery, obviously). :f6:
http://www.insoya.com/bbs/zboard.php?id=...sc&no=8117
Another thing I noticed is the description on Amp in the video says +120% damage, not +135% damage, unless that's just a typo like Fiel said (plzplz be a typo).