Zombies play wooden door breaking sounds when attacking copper doors

The Bug:

Zombies play wooden door breaking sounds when attacking copper doors.

Steps to Reproduce:

1. Summon zombies until you get one that is capable of breaking copper doors.
2. Now get the zombie to start breaking the copper door.

Expected Results:

Copper doors use unique sounds when it is getting broken by zombies.

Observed Results 

Copper doors use wooden door breaking sounds when it is getting broken by zombies.