When I married Marcurio, he would carry around a ton of stuff for me, albeit he always griped about it. Now, he won't even carry an amethyst--he believes he's already overloaded. I've removed everything from his stash except his armor and weapon, but he still thinks he's overloaded.
I have noticed that his "Store" is filled to the brim with stuff, a lot of it old things I used to have him carry. I suspect that he's carrying his "store" around with him and thus has no weight limit left to carry stuff for me. I would test this out (by buying all his store goods) but I just bought a house and land and don't have the ready cash.
Anyone else seen this problem with a married ally?