Basically, the bug goes something like this:
You ask maximizer to maximize (for example, Muscle as a Seal Clubber). It suggests creating / equipping 2 of the same weapon, since you have Double-Fisted Skull Smashing and can hold 2 1-handed weapons (say, a pair of Meat Tenderizers are Murder, since you have the ingredients on hand to make 2, your maximizer is set to suggest creating equipment if needed, and you do NOT have any on hand). It creates the 1st weapon and equips it. It then, for reasons I cannot fathom, tries to equip the weapon it just created in your off-hand slot instead of the main hand. This fails, since you can't hold a weapon in your off-hand without also having a main hand weapon; furthermore, the entire maximization execution gets aborted as well.
What SHOULD happen: Maximizer should go create BOTH weapons if it needs 2, then equip them.
Tested in KoLmafia r16228 (latest version as of this post).