For whatever reason, the items I placed on Curie's lab shelf stay, but when I started adding tools to the tables (microscope, scales) they fall through, as well as ONE beaker from the shelf. Everything else is fine.

Maybe the more items you have, the later ones fall through things further or something? I don't know. (I DO know the mannequins in Skyrim would load without their AI disabled for a second, which is why they 'move', so this may be related.)