why do my soldiers keep farting instead of gaining mana

[mib]

i've got two just hanging about that i dont use (might fuse them into another character at some point) , and they just never gain mana.

[Fel]

What each class does when left alone on the island varies, soldiers do absolutely nothing as far as I know (which includes not gaining mana).

It isn't all that hard to give them mana by fusing a good item into them (either from a high level dungeon or a "combo" item from a dungeon reward), and what other classes on the island gain is usually marginal at best, so you are not losing much from this.