OK, so I was working in creative on a map I really needed to back up, and changed to survival to kill the excess of cows I spawned (I didn't want to accidentally break stuff I had already set up). I changed back to creative, but now I cannot break or place blocks. When I break it, it "breaks" and disappears, but when I try and walk on top of it, it block-glitches like an unloaded chunk. What's really weird is when I right-click on it with anything, even an open hand, it places back the original block, as if it never got broken. I thought this was a random bug, so I restarted FTB. I opened up the console this time, to see if it would say something like "error: failed to break block" or something. Even in Debug mode, no abnormal info from the console, and the problem remained. I thought to check whether it was from the save file or my FTB installation, and it did not occur there. The console is now logging this on loading though (it wasn't logging it before): http://pastebin.com/aYge2xdq. I can't figure out what's going on. All it says relates to the builder, which I haven't put anywhere in my world. I think this is a Forge-related issue, but I'm not sure.