[1.6 AFFECTING LIVE] Horses/Donkeys/Mules are missing ears when using the horseV1 model

Verification builds:

Ver. 1.6.0.15 Release_1126522

Summary:

When using a Resource Pack which uses the old horse model, donkeys, mules and/or horses will appear without ears when the world is loaded. If you minimize the game and then open it up again, ears appear correctly again.

Impact:

Mobs missing ears

Repro Steps:

1. Download Stone Age Texture Pack from the store
2. Create a world and summon donkeys, mules and horses.
3. Either horses or mules/donkeys (doesn't seem to happen to both consistently?) will be missing their ears. 
4. Minimize the game to force it to lose focus.
5. Maximize the game again and notice all ears are now visible.

Observed Results:

Donkeys/Mules and/or Horses appear without ears when first entering the world.

Expected Results:

Donkeys, Mules, and Horses should appear with ears.

Screenshots/Videos attached: 

Yes

Regression Build

Latest version it works in: 1.6.0.5_rc3-16

Earliest version the bug appears: 1.6.0.6_beta-17

Notes:

See attached video for demo and note the regression build info. Also not sure if it works with v2 horse model or just v1. Will update this bug if I find out.