That's right. You can't fix it, because, under the current structure for messages sent via IRC there's nothing broken.
Eventually the IRC protocols might allow for longer messages, but since a 512 character message is approximately 400 characters for your actual message.
It's been a while, but if I recall correctly the average English word is 5 - 10 characters in length, thus with 400 characters available, that's a message of 40-80 words.
