Summary:

Placing some incomplete / transparent blocks on leaves disables "fancy leaves".
Works only if leaves are surrounded by full blocks (eg dirt, but wool doesn't fit, for example).

Affected blocks:

• Button
• Bell
• Dragon Egg
• Slabs (MCPE-53731)
• Amethyst Cluster (Amethyst Bud)
• Pointed Dripstone
• Spawner

Steps to reproduce:

1. Turn on the function in the settings "fancy leaves".
2. Place the leaves.
3. Surround the leaves with dirt, except for the top side.
4. Place (in any way / see the picture below) above the upper side of the indicated blocks.

Observed results:

Through the transparent spaces of the blocks at the leaves, you can see how the "fancy leaves" function has been disabled.

Expected results:

When the "fancy leaves" function is on, all leaves will be transparent.

Image: