It appears some blocks, such as marble, when you use multipart on them, have some issues with missing textures.

I have experienced the same issue. I did some testing with the latest FMP and the earliest you can let modded MC load at now (1.1.1.321), and neither helped. I also went back to Cricket's Chisel 2 and performed the same tests, and recieved the same results:

INpureCore is pretty much the best option to cull NEI of those multiparts. Out of sight, out of mind.

There is nothing we can do to fix this.