Tested with OpenBlocks-1.7.10-1.3-snapshot-479
Any headgear will make inverted crayon blocks disappear. Even a plain old Iron Helmet.

Just for more information, can you please list your OpenModsLib version, Forge Version and anything else that may assist in finding this issue.

OpenModsLib-1.7.10-0.6-snapshot-247
Forge 1208 (though I also just tested it with the latest and the same thing happened)
Edit: I had no other mods loaded in my testing instance