That is because the high oven, apparently, only smelts stuff [that] is oreDictionary'ed to ore. Dusts are, Sand and gravel are not. They used to be, but, well, you should be able to see the problem with having an ore gravel, sand, and dust with the same ore dictionary tag plus having several items in AgSkies that can unify based on ore dictionary. Massive, massive exploit that I just realized for my own pack and closed.
Thanks to the magic [of] Modtweaker you could re-add ore gravel and ore sand to the stuff that the High Oven can smelt. I'm not sure if Jadedcat will bother, as it was a pita to do (btw, Jadedcat, if you'd like to borrow that code, I'd gladly send it to you, you would need the latest Modtweaker, though).
Honestly, though, thanks to the packager it isn't that big a deal to work around. One activator to place the ore gravel and sand, another to smack it with a hammer, the packager to make all the bits back into blocks and a bit of duct work to route things to their proper places. It is a neat challenge.