Well, I can probably explain why they're looping back. What I don't understand is why you have a tube looping back in the first place. Is there anything at all you want to be traveling in that direction?
Anyway, as for why stuff is looping back, well, it's because you have tubes looping back. The way RedPower works is that everything heads to the closest available inventory that can accept it. If an item is tagged with a color, then any other tube colors are basically cut off. If you have a tube looping back to the first sorter and your storage is as far away as it appears to be, then the closest inventory IS your first sorter, and stuff will loop back.
Oh wait, I think I literally JUST figured out what's wrong.
Is your last sorter in the line also set to tag items it can't sort as white? And I'm assuming the outputs of your sorters are all connected to each other so they all go in the same direction towards your chests. I think I've got it. You need a few restriction tubes, but ONLY a few. Have each sorter output into a normal tube. That normal tube should connect to a white tube that links to the next sorter, and a restriction tube that links to the chests. The restriction tube prevents white-tagged items from the last sorter from moving backwards into a previous sorter.
Basically, do this (sorry for my lame diagram)
Code:
S
|X--|
W |
S |
|X--|
W |
S |
|---------------Chests
S = Sorter
| or - = tube
W = white tube
X = restriction tube
This can be extended for however many sorters you have. Just make sure you have a restriction tube between each sorter and the pipe that connects all of the sorter outputs (the last sorter doesn't need one after it though). Also have a chest that's a valid destination for white-tagged items from the final sorter, or it'll go back through the restriction tubes anyway.
You could also replace any of the restriction tubes in my diagram with a transposer (make sure the side with the plus on it faces the sorter side of the network), which achieves more or less the same effect by serving as a one-way tube.
EDIT: I fail at making things in Code tags line up. Fixed.