The Chassis on the left has a QuickSort Module with no upgrades, and the Basic Log Pipe on the right is set to not be the default route, with a whitelist of Stone. The chest on the right is full of Stone.

If I put Stone in the left chest, it sends out one stack of Stone, which gets stuck in the Basic Log Pipe. But when it gets there, the QuickSort Module sends out the rest of the Stone in the first chest too, several times a second.

Then it builds up, then eventually pops out into the world

When another Chassis is added with a Terminus Module, items still get sent to the right chest but then get bounced to the Terminus. Is this normal behavior?

Hmm, replacing the QuickSort with an Extractor does the same thing. I suppose this is intentional, sorry.