When any non-symmetrical pattern is applied to a banner, it will appear mirrored on the backside, but for the "Field Masoned", "Skull Charge", "Flow", and "Guster" patterns, this is not the case. (images contain "Thing" and "Globe" patterns for reference)
(for guster it is only noticeable on the bottom 4 pixels of the texture)
Attached is a resource pack containing fixed versions of the textures.
Can confirm