Messing around in FTB Infinity Evolved's latest version (2.3.5), I've found a bug that allows duping of blocks in an interaction between OB and Chickenbones' Translocators mod. I have no idea which mod it would be originating with, so I figured better safe than sorry, report it in both places.

If you press 'C' by default while looking at the ground with translocators, it places a crafting grid on the ground that you can use to craft items in-world. If an OpenBlocks /dev/null that is filled with blocks that can be placed in the world is set in the crafting grid, and the grid is then broken (either by punching it or pressing 'C' on it again), two /dev/nulls with the same inventory amount pop out.

It doesn't work with any blocks that cannot be placed, so you couldn't dupe normal diamonds for example, but you CAN dupe blocks of diamonds... blocks of draconium... anything you can place, really.

Have you tried a diamond pickaxe? (On the in-world crafting grid)

No I mean like without a /dev/null.

I have, it doesn't dupe anything that cannot be placed in the world as a block (or entities, though i haven't tested a lot of those. For example, it will dupe stacks of torches. It will also dupe Resonant Pulverizers, but it will not dupe pickaxes or swords)

A good barometer seems to be when you place the /dev/null into the crafting grid; if the object inside the /dev/null is not visible inside of it when it's in the crafting grid, it doesn't seem to dupe, but if you can see the object inside once you place it on the grid, breaking the grid will pop out two of the /dev/null.

Not sure if you mean crafting or placing a pre-crafted one into the grid, but both seem to operate as expected, no duping.

What about placing on a vanilla crafting table and closing the GUI?