Environment And Mod Information:

• Minecraft Version: 1.12.2
• Forge Version: 14.23.5.2854
• Doggy Talents Version: DoggyTalents-1.12.2-1.15.1.5
• Heat And Climate Lib Version: 3.3.3
• Heat And Climate Mod Version: 3.3.8

Steps to reproduce:

1. Take a Doggy Talents puppy, give it Pack Puppy skill.
2. Take one type of containers from HAC. I have tested all kind of Lowchests, Wallshellves and Three types of HAC chests:
   Villagers' Chest, Steel Chest and Magnet Chest.
   For this experiment, 2 container from any one type above is enough.
3. Fill one of the containers with the item you want to duplicate, spare the other.
4. Give the empty one to the puppy.
5. Then, Give the filled one to the puppy.
6. Take the two containers out of the puppy's inventory.
7. Open them, and find that two containers are filled with the same items.
8. If you do the 5th step before the 4th step, you will get 2 empty containers and lose the items in the filled one.

Additional Information:

I will post the same issue to Doggy Talents Mod too: percivalalb/DoggyTalents#249
But I think it necessary to post this issue here, because this issue is only seen with that Mod's containers now.
Thanks in advance for your kind-hearted help.