If the unlocalized name has caps I found that the assets no longer load outside of the dev environment. Happened to me as well.When making a 1.8 mod recently this was a problem for me, actually, so I'm not sure about 1.7.10 (although I don't remember having the problem in that one). The block was called fluxDuct, the assets folder was named accordingly, and while in the development environment everything was perfectly fine. But for some strange reason, after I built the mod and ran it in MultiMC, it couldn't find the assets anymore. I wasted an hour of my life trying to figure out what in the world was going on, until I made it all lowercase and suddenly it was fine.
Also, the capitalization will definitely make a difference when specifying the localization in your language file.