I know that the "extra huge" mushrooms is a cool feature added in 1.10 but I found a generation bug that only works with "extra huge" mushrooms, their stem won't grow an odd number of blocks tall (if your counting the top of the mushroom, the whole mushroom wont grow an even number of blocks tall). I found many huge mushrooms and measured their stems, only the mushrooms that were more than 7 blocks tall had this bug. In the screenshots I added glowstone to make it easier to observe the heights of the mushrooms.

its simple to reproduce: look for huge mushrooms more than 7 blocks tall and observe their height, you will see how I described them.