Mangroves don't always grow on mud

I was messing with mangroves and noticed they don't seem to consistently grow on mud.

working:

not working:

Even with the random tickspeed up and the same sized platform, it doesn't seem to grow. The second grew without issue once I turned the platform to grass blocks using /fill.

More tests may need to be done to see if there is an exact reason that I haven't pin pointed yet, but currently this seems wrong.