I was wandering around in my survival world when I saw that a mangrove root hadn't generated. I noticed there was a lily pad just below.

I tried to reproduce this myself and I saw thanks to my experiments that the mangrove roots trees cannot grow on lily pads.

Unfortunately, I don't have more details about this bug... But I think that lily pads TOTALLY prevent the generation of mangrove roots and that makes minecraft less beautiful :'(

If you can fix this bug at least in the natural generation of the game, that would be perfect please