Not sure if it's still present in modern Quark mod versions, but in 1.12.2 a dupe bug was persistent with the use of stonelings.

The steps to reproduce this bug is as follows:

1. Tame a stoneling
2. Give the stoneling the item you want to dupe (can have NBT data, i.e. shulkers and and bundles)
3. Bring the stoneling to 1 hp
4. Press shift into crouching
5. Press LMB and RMB at nearly the same time. (LMB must be first)
   The result is that the stoneling drops the item it's holding, while also giving the player the item it held. This behavior can be easily tested in older 1.12.2 versions, but has not been tested in newer versions yet.

Giving the stoneling a minimum of 2 Heart of Diamonds in a storage item like a shulker or bundle with other items result in a infinite duplication glitch.

Note: I'm not the person who found this glitch

this doesn't seem to be happening in 1.20.1, you can't retrieve the item in the death animation and picking up items from the stonelings seems to make them immune for a second.

this doesn't seem to be happening in 1.20.1, you can't retrieve the item in the death animation and picking up items from the stonelings seems to make them immune for a second.

Thanks for the clarification.