The nether plants like saplings, mushrooms, bushes, flowers.... from other mods like Biomes O Plenty and Ad Inferos can't be placed on tainted soil and heat sand while they should.

The Blocks from Ad Inferos can't be placed on tainted soil or heat sand because Ad Inferos doesn't check if it can be placed on natura's blocks. As for Biomes O Plenty, I can put their glowshroom's down on Tainted Soil and Heat Sand. If you can, what blocks form Biomes O Plenty can't you place on the Tainted Soil/Heat Sand?

The easiest would be I report it directly to the BOP and Ad Inferos modders.

Okay here is the list of all the nether plants from BOP and Ad Inferos

• Biome O Plenty
  • Hellbrack tree
  • Devilweed
  • Deadgrass
  • Thorns
  • Burning Blossom
  • Eyebulb
  • Glowshroom
  • Toadstool
  • Blue milk cap
  • Flat Mushroom
  • Portobello
  • Ivy
• Ad Inferos
  • Inferno tree
  • Magma tree
  • Phantom tree
  • Ash tree
  • Purple Mushroom
• NetherEx
  • Brown Elder Mushroom
  • Red Elder Mushroom
  • Enoki Mushroom
  • Thorstalk