Problems with "Ghost Blocks" and /fill command

I'm experiencing problems with the /fill command being run through a command block, because when the command is executed, it doesn't fill the specified zone (from X=-1914, Y=87, Z=-1413 to X=-1915, Y=87, Z=-1414) with the intended block type I was using to fill, which was supposed to be blue wool.

Instead of blue wool, I got a pocket of air, or "ghost blocks". When I ran the same command in the chat text bar, it executed the command just fine, but it wouldn't do the same from a command block...