Alternative textures for seasons don't work if a resource pack that requires Continuity is installed.
I tried creating my own texture for my bushy leaf block, but I realized the "seasonal lush cave" texture pack doesn't work at all.
I hope this is fixed and, if possible, added support for compatibility with Optifine's texture methods. (I think it's best to report this to the Optifine creator.)

One more thing: The alternative texture definition doesn't work if the original model is defined in the blockstate using a model array (to create random textures).