EDIT: It's a bit too large to copy/paste easily.
If you still have the zipfile, you can extract again and put the data/init/interface.txt from the fresh folder into the same place in your old folder.
If that doesn't fix it, you'll probably have to do a fresh install (which you've just done anyway) and apply your mods, graphics, and save into your new folder.
If THAT doesn't fix it, it's likely a problem with your computer or keyboard.
I've tried replacing the interface.txt but I haven't done the fresh install, at this point I think thats what I'll try.
edit: well it appears the fresh install worked, something must have altered when I copied it to the usb because there was one point where it told me there wasn't enough room and had to do it over *shrug*. Anyway I wasn't sure about posting it in bug forum since it may of had to do with the 40d11 version which, technecally, I see as having not to do with toady.
edit 2: scratch that, went back to accually play and it started to do it again. I likely has to do with the save file doing something to the game yet the regular DF (non 11) seems to be completely fine even with the same save file. So its either the save, the init file (copied that from previous game), or the tileset files somehow partially corupting. At this point I'll wait till tommarrow to do some more testing.