I have a sorting system based on advanced item laser relays ending with a catch all item laser relay (not advanced). When I put a single item into the system that is not caught by the sorter, I get 1 stack (sometimes 2) of the item in the reject chest attached to the catch all item laser relay.

If you disconnect the ESD from the relay above it and move them a block apart, does it stop happening?

Yes, your suggestion has stopped the behavior. Cheers.

Yeah, it's still a bug that I don't understand.
Dang it.
I'll close this for now but I'll keep it in mind.

Can't reproduce.

What Minecraft version?
What other mods installed?
What type of chest?
Give me some helpful information please.

MC: 1.10.2
Other mods:
EnderBags-1.9.4-2.0.0.jar
jei_1.10.2-3.7.3.221.jar
Ping-1.10.X-1.2.2.B7-universal.jar
teleporters-1.1.3.jar
thutcore-1.9.4-3.1.8.jar
thuttech-3.0.5.jar
ActuallyAdditions-1.10.2-r49.jar

Type of chest is a small crate.

Happy to upload the world somewhere for you if you would like.

Or you could join my server and check it out if you would like.

Still can't reproduce.
What are you inputting with?

input is a small crate -> esd -> item interface -> item laser relay -> advanced item laser relay ......... -> item laser relay small crate.

the chain AILR chain looks like:

SC <- ILR -------          AILR -> AILR -> AILR -> ....
                 \           ^       v       v
                  \        AILR    AILR    AILR
                   \         ^       v       v
SC -> AESD -> II -> ILR -> AILR    AILR    AILR

Each of the AILR are filtering for 1 item.

All AILR are feeding into small crates.

Yea I don't get what you're saying.
Please just make a video or a couple of screenshots.

http://imgur.com/a/ONxnX