Not to troll or anything, but the Twitch docs do indicate:
PRIVMSG: Sending a message
PRIVMSG #channel **:**Message to send
As you can see, the colon is required before the message and tduva is right, that is the IRC standard. When I was working on rewriting an IRC library for my bot I stepped back, captured all the messages from Twitch and did some light reading on the IRC standard as well as the Twitch documents for their specific deviations from the standard.
That deviation can sometimes cause heartburn for sure.