Not sure about your theory, unless things have changed significantly in the pre-release version I'm testing with (which is possible).
I just added 5031 files to collections, both into lots of sub-collections and then into a single collection, but the collections folder is using just under 1MB and the memory usage increase was nowhere near 600MB.
Normally I'd assume high memory usage like that was probably due to a shell extension, video codec or plugin going haywire over some of the files (more info here), but the huge collections folder suggests something else might be going on.
Is this something you can reproduce? If so, could you zip your collections folder up so it can be looked at to see why it's using so much space?