Utilizing these specific conditions:

A Storage Drawer from the mod Storage Drawers as the storage (cannot be replaced by any other storage method, like a vanilla chest)
Pipez's Item Pipe as the transfer method
Any IC2 Classic block that has multiple item slots as the receiver (Tested with the Machine Buffer and Nuclear Reactor, no vanilla storage block/Storage Drawer as the receiver has this issue)
The item being transferred is unstackable.
Specifically the issue seems to revolve around the fact that base Item Pipes transfer 4 items every 20 ticks, which is why one item turns into four items.
Unsure why the receiver has to be an IC2 storage block though. Or why it only takes 1 item at a time from the storage drawer.

Steps to reproduce:

Any Storage Drawer with at least 2 of an unstackable item in it
An IC2 Block that has multiple valid storage slots (Machine Buffer is easiest)
A Pipez Item Pipe connecting the two blocks
Make the Item Pipe extract from the Storage Drawer
duped items end up in the IC2 Block.

Video reproduction: https://youtu.be/lAVPtgiGLJs

Also reposted in the issue trackers of the other two aforementioned mods:
TinyModularThings/IC2Classic#1319
henkelmax/pipez#283