Create a custom banners using a loom (try making it as complex as possible), add it to a shield and save it in a hotbar, then, change your game to a higher version. The banner on the shield doesn't load properly and lowers its resolution.

Expected result: The shield displais the original banner

Observed results: The shield shows a lower resolution version of the original banner.

This can affect any world or version in witch you can obtain a customized shield from a hotbar save.