If you have Tubers bag and its "2x" above your head and you will take

, "2x" image from tubers bag is replaced by image from

, and when you go to next level, you cannot ever see that "2x", but you still have double score. I think it works same with all other items that have image above your head like

or mariomode. But tubers bag is only one item that has image effect above head for more levels, so you can see it only if you have tubers bag and take another "head image" item.
another discovery:
When you go to the next level, game is programmed so that igor always "teleports" from bottom of screen to his original place (often to the top of screen, because you are falling from top). I saw it when I had tubers bag. because with tubers bag you have above head "2x" or "x2" image, every time you go to the next level, you can see that "x2" very quickly flies from bottom of level to igors original location ´(often at top), and than you see igor. It works same when you teleport to some level by blue portal or door (from PD or to PD). Image with "x2" flies from bottom to the location, where igor appears. when i will get my next tubers bag, i will try to film that!(it will be 5th) probably, igor is not teleporting from bottom, but only that image ("x2")