What you describe only appears to be. The reason no one chats for a long time is because you were disconnected from the server. Only it forgot to tell you for some reason. It happens to me regularly, especially when I have some proggies running that gobble a lot of bandwidth. To everyone else in the channel, you're long gone. When you type something, mIRC tries to send the text to the server, notices it isn't there, concludes it itsn't connected anymore, and tells you it has disconnected.
You can't really fix it, as the getting disconnected part is mostly not in your control. All I can think of is to write a piece of code that someway checks if you're still online without flooding or abusing the server.
