Affects either / any stamp. I've got a crafttweaker script to melt Constantan ingots/plates into 144 mb of molten constantan, as well as stamp one ingot or plate from 144 mb with the respective stamp. -
nothing to do with crafttweaker- it affects all materials. The only requirement is that the stamper must have a stamp 'equipped' while it's receiving fluid- the bug does not occur if the fluid is pumped in while no stamp is set.

Not quite sure what's going on with the stamper- I have a fluid gauge attached, and after it stamps out the first ingot, it displays '24/1000', suggesting that it's only consumed 120 mb, even though it should have used 144mb- and it then continues to produce another ingot with that remaining 24 mb... Furthermore, if I put 3 ingots in the melter, I actually get 4 ingots back out the stamper, so it's more like the bug's only occurring on the 'final' stamp rather than an actual 'dupe'...

Versions:
Forge: 14.23.3.2675
Soot: 0.15

jesus what
i will investigate this soonish

Hang on. Just noticed this has nothing to do with crafttweaker! I can dupe any ingot by simply re-melting it. Investigating some more...

Okay, I've isolated the mods to eliminate any chance of external incompatibilities. Been looking into it & it seems to get weirder: it only affects stampers that have already have a stamp while receiving a fluid to stamp out. The dupe does not occur if I load up the internal buffer of the stamp base, and only then attach a bar stamp after I've finished pumping the fluids over.

It affects any materials / stamps, and occurs regardless of whether there's a bin under the stamp base- as long as the stamper has a stamp equipped to it before the fluid is inserted.

I think I know exactly what's happening. The problem is that fluid matching is amount agnostic. I will fix this when I wake up.