Odd problems with Penumbra Collection?

[Blurz]

I just bought the Penumbra collection, for the convenience of having the series available on one disc, but I've noticed quite a few glitches that don't happen on my standalone copies of the three games. Sometimes objects or walls will be transparent or missing entirely. The weird problem is occasionaly the first time I enter an area with movable items, the size will change (they will function the same as the normal countrerpart though). This happened a LOT in the first few rooms- the book of explosives was large, and the shoes were massive, which was pretty funny. I've had the transparent item/wall thing happen on some games before, but never change of an object's size. Does anyone have any ideas as to why this happens?