MCA + Mo'Creatures = a dangerous world for hapless villagers. I've started up a graveyard to remember them by. But tombstones are being super weird.

1. Craft a tombstone. Works fine.
2. Place tombstone. Tombstone is placed, and then there is a stack of 2 in your hand.

3. Place Tombstones out of the stack of 2. They continue to duplicate into the stack.
   

4. Mine the tombstones back up, they will not stack in the original stack or with each other.
   

5. Place Tombstones from one of the "non-stacking" tombstone items, the duplication begins again.
   

I ended up with 35+ tombstones from just trying to place a few on the hill~!

Mods:
forge1.12.2-14.23.0.2495

BetterFoliage-MC1.12-2.1.10
BiomesOPlenty-1.12.2-7.0.1.2298-universal.jar
chococraft_1.12.1-0.9.1.52.jar
CustomMobSpawner-3.11.3.jar
DrZharks MoCreatures Mod-12.0.3.jar
DynamicSurroundings-1.12.2-3.4.7.2.jar
journeymap-1.12-5.4.9.jar
JustAFewFish-1.7_for_1.12.jar
Mantle-1.12-1.3.1.21.jar
MCA-1.12.x-5.3.1-universal.jar
Natura-1.12-4.3.0.17.jar
PetBat-1.12.jar
RadixCore-1.12.x-2.2.1-universal.jar
SoundFilters-0.10_for_1.12.jar
TreeChopper-1.12.1-1.2.2.jar

Odd, will look into this.