I don't get why weapons can be sheathed but shields remain hanging on the arm.

There's a mod called http://steamcommunity.com/sharedfiles/filedetails/?id=10451 but the shields are in fact arrows/quivers and no armor, so this mod is only for cosmetic reasons. It shows how a future mod or patch could work.
Really hope there will be a patch that includes shields to be carried on the back when you sheath the weapon. To avoid clipping with quivers simply disable showing quivers on the back when carrying a shield.
Regards
