It's not bugged, it is just not optimal to use that lining in combination with sturdy boiled leather armors.
The base property of all ancient dire hides is to provide a +2 AC vs Piercing at the cost of a 10 pounds weight increase. The benefit is nullified by the base +2 AC bonus of the sturdy boiled leather armors, but the weight remains. It is still of value on armors made of chitins or metal.