on a dedicated server, If you access an Arsenal by double-clicking on it in Vicinity rather than by pressing "F" to access the Arsenal directly, any US vest you equip by RIGHT-CLICKING will report being at 200% carrying capacity and be unable to accept any items. DRAGGING the vest to your paper doll slot instead of right-clicking will, however, show the correct 0% carrying capacity and will allow items to be placed in the vest normally.
This behaviour is not exhibited by the FIA or Soviet vests, nor is it exhibited in a local, singleplayer Game Master session.