Ok so I was on my creative world again, and  I had a command block with the command:

/say Oopsy!

and that worked fine, and the command block with the exact same command in it said:

 Unknown command: say. Please check that the command exists and that you have permission to use it.

How to reproduce:

1. Place two command blocks next to each other facing the same way (not into each other).
2. Type this command into the one on the left and activate it:

 /say Oopsy!

3. Do the same with the one on the right.

Observed results: The command block on the right doesn’t do the command, because /say “doesn’t exist”. 

Expected results: The command block on the right does the same as the one on the left.