Unequipping these seems to drain spellslots, EVEN IF they are not bonus slots. I have 7 level 1 spells per day, and 3 bonus level 1 slots.
When one of my items is unquipped, it kills a slot. I have done this 5 times in a row and it eats the slot even if it is not a bonus spellslot. Normally this is not usually a problem, but on quests like harpies or so, it can really mess you up when those charms make you unquip/re-equip your weapon and things randomly!
This is a BioWare thing.