Command block sets incorrect block

The same command block produces incorrect color.  Thinking this was a bug in my 2-D printer, I placed a button next to the command block: when you press this button, the command block creates the correct color of wool.  I placed repeaters behind each command block in my contraption to demonstrate that redstone is powering the correct command block.

Because I know this sounds implausible, and I know my own groups reaction to insane sounding claims, I attached a minute video demonstrating the issue (clumsily - I'm sorry about that).

The version reported on the start-screen is v1.6.0

Thanks,
Mark