If a block is placed directly above a bamboo mat, the bamboo mat becomes transparent and gives the player an x-ray view into the ground. Also related to the bamboo mat, I believe the viewmodel should be moved up slightly so that it is in the same position as carpet blocks. As it is it mostly cannot be seen as it is too far down and off the screen.

Also, this isn't really a bug report but more of a general question, but is the foxhound's tail intended to wag up and down when it walks instead of side to side like the wolf's tail?

I can't reproduce the x-ray issue

Must be optifine. I doubt the optifine dev is gonna care about one bug in one mod though, so I'll just put up with it lol