I never met any possible "bug" with the body parts.

To be "sure" I don't add a body part I do not wish to use by the Necromancer Naberius I write down the current bodyparts my Creature has and compare this with a body part I find. If I don't like it, I sell it (yes, I always CAN sell "crappy" body parts!!), otherwise I go to Naberius to make my Creature stronger ...
OR
I write down where I found the bodypart (chest, loot) and leave it for later on that place ! wink
(I do this with many items/loot to have more control over my Inventory space)

On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin,
it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !