Mipmaping Broken

Mipmapping is completely broken, and things look awful.

To recreate: the bug occurred after splicing together two resource packs to add textures for the new blocks and items. After selecting the edited pack, mipmapping failed. Subsequent attempts to fix the issue, including reverting to the default pack and changing to the unedited pack, have done nothing to help the issue.

EDIT: Switching to the default resource pack and then quiting and relaunching Minecraft fixes the mipmapping bug, but switching to the resource pack breaks it again.