If you switch resource packs and then take armor off a horse the horse will still appear with the armor on. This is how to duplicate:

• Use any resource pack (I used Faithful 32x32)
• using a spawn egg spawn a horse
• tame the horse and saddle it
• put armor on the horse
• switch to the default resource pack
• take the armor off the horse
• observe the armor texture still on the horse

This is a duplicate of MC-18813 but it was closed and I didn't think a comment would be seen.