There should be more detection for which half a copycat slab is on, and whether its facing E/W or N/S or Up/Down, or if it has another slab next to it or a slab gap.
I've fixed some of the more obvious errors, but because of various limitations in the existing copycat mechanism, connected textures on copycats can never be 100% perfect.
There should be more detection for which half a copycat slab is on, and whether its facing E/W or N/S or Up/Down, or if it has another slab next to it or a slab gap.