Thank for playing!
That was a design decision - I even thought to make the inventory smaller to better justify the drop mechanics and to force players change cloths/take-drop items more often and face " damn, cant take new items, forgot to clean the inventory" moments :D
The more witch cloths you put on - the less chances they notices you. Or actually the longer time you can walk around unnoticed :)
The same for any monster rooms. But walking with zombie/vampire/ghost cloths in the witch room give you no extra protection at all! Plus they may steal the cloths from you (and it spawns back to where it was stored initially). Because at the end - no one is invited unless you are a member of their monster group :D