(Posting in Questions in case anyone searches for this topic later, though I've actually figured out a workaround for the problem.)
So I had one military dwarf, Thikut, assigned to his own squad, and he who wore all his armor properly. Later I drafted two more dwarfs, Vabok and Iden, into a new squad for training, but they only wore one gauntlet each. So I told them to remove all civilian clothes, and reequipped them over and over. If they just randomly put their armor on incorrectly, they'd eventually do it the right way, right? No dice. They refused to wear two gauntlets no matter what. I started reforming the squads- one squad, three squads, different captains, etc., and noticed that no matter what dwarf was in what position, the first to equip would always wear wear two gauntlets, the second would wear a left gauntlet, and the third would always wear a right gauntlet. Wtf. It wasn't just that these new recruits were retards, because if Iden was the first to equip, he'd do it properly and Thikut, the original dwarf, would be left with one gauntlet.
Slot #2 and #3 in the military list always divided one pair of gloves between them.
So finally, I put the Thikut (#1) in his own squad and equipped him. Then assigned my two mechanics, Kib and Shorast, to be in an active/unscheduled squad (#2 ) equipped only with gauntlets. They each put on one gauntlet as the others had. Then I assigned Iden and Vabok (now #4 & #5) to Thikut's squad and, miraculously, they both put on their gauntlets correctly. So I didn't stop the bug, i just passed the problem off to some non-combatants. Now Kib the creepy-girl mechanic (the one with the pet roach) is walking around my fortress starkers except for a masterwork steel glove and a smile. I imagine she gives the other mechanic clanging high fives in the hallway and everyone cringes.
Other people have had the one-gauntlet problem, and MAYBE this would work for them. This is 31.12, but I doubt this bug has been fixed as of 31.16.