Not sure if this is caused by JEI. Mods I have installed are Climatic Biomes 2, Biomes O Plenty, Biomes You'll Go, Traverse, Novam Terram, Underground Biomes, and a bunch of others that I don't think have to do with it.

The moment I installed UB, I noticed that whenever I encountered large mountains, they were partially made up of White Skyris Leaves blocks from BYG.