And their carrying capacity goes down because the game keeps adding an unplayable hunting bow and twelve unplayable arrows to their inventory when you recruit them. The bad news is that they'll use that bow instead of one you give them. The good news is that they'll use what arrows you give them, and as long as they fire from that unplayable bow, their arrows are infinite.
You can remove it on PC with "removeitem 10e2dd 1" until the text spam indicates that they're not carrying any (for the arrows, it's "removeitem 10e2de 12", but arrows are weightless). Literally no way to fix that on Xbox or PS3. You can, however, complain to Bethesda, and it's actually likely that they'd fix it, since all it would take is to either remove the two script lines that add the bow, or add two script lines that remove the bow when they're dismissed.
Honestly, the fact that their arrows are infinite when using that bow seems like an exploit to me, and it seems like unitended behavior (else, why add twelve arrows when one would have sufficed?).

