Comma or other symbol after @ selector does not work with command blocks

@p and @a won't list usernames

What I expected to happen was...:

Command Block: /say @p, You are not allowed to access this area!

What actually happened was...:
[@] @p, you are not allowed to access this area!

Steps to Reproduce:
1. Get a command block (/give username 137)
2. Type in the command block /say @p, somat here
3. Power with redstone

Result:

[@] @p, somat here