I made a small corner of iron furnaces in my house. Upon disconnecting from my server and reconnecting, the texture and face of the iron furnace changes to what looks like a machine block.
Activating it doesn't fix it, making it start smelting/cooking doesn't fix it, placing blocks around and then removing them doesn't fix it either. Reconnecting to the server or reloading the game definitely doesn't fix it, that seems to be what causes it. (I read about similar problems but these were the suggested solutions and none of them work)
If I remove the furance and rebuild it, it will then properly show what it is, until I reload the map anyways.
Thanks in advance for any suggestions 
Curiously, I can get on SSP, build iron furances, then reload that map all I want and the faces won't disappear.
Besides iron furnace, I've only built a macerator and a geothermal generator, neither of which have this problem.
A friend that's playing with me is also reporting to me that he's seeing the same thing: it looks correct until you rejoin the server.
On my server I have:
ModLoaderMp 1.8.1 Server
ModLoaderMp-server fix
minecraftforge-server-1.1.1
I also have build craft, but the problem persists wether it's active or not.