Models Banners bug

^{Update by [Mojang] Mega_Spud (Jay Wells):}
Summary:
Adding four or more layers to a banner will result in parts of it being invisible. It looks as though previous layers get overwritten, and become invisible.

Steps to Reproduce:

1. Create a banner
2. Keep adding layers of detail to it

Observed Results:
When you add four or more layers, the previous layers start to become invisible.

Expected Results:
The banner should just keep adding new layers on top, and not cause lower layers to become invisible.

Screenshots/Videos attached: Yes

Notes:

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Original Description:
Using the banner, i'm craft a special banner, and the textures banners has bugged.