Can confirm this. Just did a quick test in Singleplayer:
- Set Item Spoil Rate to 10.0 for faster decay
- Place a Compost Heap for further speeding up the item spoil
- Place some cubs/spiderlings into the Compost Heap and wait until 5sec are left
- Take the cubs out of the Compost Heap => around 1:30min left
- Place the cubs with food in the Animal Pen for training (Tier doesn’t matter. I did it with T3 Pens)
- Watch them die within 1:30min
Suggestion: make items or even better cubs not spoil within the Animal Pen (like you did with the preservation box)