I can give a companion a weapon with mods attached and they'll equip the weapon, but the model of the modded weapon doesn't show the attached mods when it's on my companion. I noticed this when I gave a Cowboy Repeater with 3 mods attached (+4 ammo, decreased weight, less time between shots) to Boone with .357 ammo and he equipped it but the mods were not visible on the weapon. I don't know if it's just a graphical bug and the mods are still working even though they're not visible, but I have no way of verifying this.

Also, when flipping between inventory types while bartering, the other person's name disappeared.