Cows, Sheep, Pigs, Chickens and Rabbits (and probably other mobs too) are able to see a nearby player through blocks (opaque and transparent), if that player is holding the food the mob likes.

All mentioned mobs were able to detect the food through blocks. Other mobs aren't affected by this bug. Untamed Wolves for example won't react to a player holding a bone or food behind a wall.

I did not test this bug with all breedable mobs