If a cat sits on a chest then the chest is blocked, this is normal behavior, but it also affects the chest under the one the cat is sitting on, so 2 chests are affected.
Steps to reproduce:
Place a chest
Place a chest on top of the first chest
Put a tamed cat on top of that
Notice both chests are affected
Expected Behavior:
Only the chest the cat is sitting on would be affected, not both.
this is most likely WAI as using other none full blocks above the chest achieves the same effect