Trying to create high-resolution versions of the images in assets/minecraft/textures/entity/banner

I created high res version some images. When I reload textures, banners that showed those textures became blank. Changes to the images without changing the resolution worked as expected.

What I expected to happen was...:
I expected to see the higher-resolution versions I had created.

What actually happened was...:
Blank banners

Steps to Reproduce:

1. Create a custom texture back that contains a duplicate of the default resource pack in assets/minecraft/textures/entity/banner
2. Create a banner in your world that has the Mojang log texture. Place it in the world.
3. Notice that the texture is what is expected
4. Double the resolution of assets/minecraft/textures/entity/banner/mojang.png to 128x128 and save
5. Reload your resource pack.
6. Notice that the banner is now blank.

I checked if this was a problem with having only one high res image by changing all the images to 128x128. The problem remained.