Legacy Custom Options settings not respected from JSON file

I know this is an entirely experimental feature, but I had to try it because we used it often in our multi-player worlds. When I use an older version of MC to create my preset, and then export the file in the latest version, certain settings such as minheight and maxheight of certain blocks are not respected. 

Steps to reproduce

1. Create single player world
2. Import worldgen settings from a preset world (attached)
3. Play world
4. Teleport to 0 80 0 in creative mode 

Expected results: diorite, andesite, and granite do not appear above level 59

Actual results: diorite, andesite, and granite appear above level 59

Other settings in the export are modified as well, but not as clearly demonstrated, so I use the above 3 blocks as an example.