Cleptomaynia

This keystone sure is interesting but also a bit troublesome to maintaine. I've tried it for one game and during that game I think I got around 7-8 unique drops. Now mind you that we only have 6 slots and about half of those gets filled rather quickly with items. The problem I see is obtaining whatever drops and how RNG works around it. Say if your slots are all filled up will the drops be restricted to whatever already exsists in ones inventory? Or will we be neglected those drops, punished for buying items?