A basic sorting system was assembled, composed by a few hoppers with rails on top.
A minecart w/chest made the duty of distributing the items along the line, The hoppers placed items in minecarts below to distribute the items into organized chests.
The problem occurs when the minecart above the hopper brings in Leather (Tried with Redstone torches and Gold Ore). The hopper won't retrieve the corresponding items from the minecart, and won't deploy them into the minecart below either.
[MC-12283] Hopper and leather on rails don't mix
The system relies on a hopper-comparator combination; exactly 23 items on the hopper allow the comparator to output 1 more block of redstone current, thus driving the piston that completes the circuit below, a simple 4-tick delay allows powered rails to displace a minecart, and once the hopper has one item taken, the current will be turned back to one, cutting the circuit, but the repeaters give the rails enough current to allow the minecart to travel a couple of blocks uphill, into the second hopper, where they are deposited into a chest.
I have found the issue. A stray redstone signal disengaged the hopper's retrieval capacities; the deletion of the errant lever that caused the problem made the system functional once again.
Thanks for your support.