When attempting to fill tnt with command blocks (I have my reasons), I encountered the bug showed on the image. The command is:

/fill ~5 ~5 ~5 ~-5 ~-5 ~-5 command_block 0 replace tnt

though it appeared through many variations of this syntax:

/fill <x> <y> <z> <x2> <y2> <z2> command_block 0 replace <any block>