That looks okay to me - mIRC v7.x added a new feature that splits long channel/query messages and can be found in the mIRC Options/Messages dialog. This feature affects only PRIVMSG messages and no other server messages. If you are trying to send a server message that is too long for the server, the server will chop the message. You will need to make sure that your message fits the maximum allowed message length for that particular server.
