Here's a post from Rowan on this very same topic dated 2006 ... it's an ongoing thing which should have been solved ages ago, such as when it was discovered that the timeout is set to 30 minutes (sorry, not the 15 minutes I assumed earlier):

http://www.bikeforums.net/showthread...ems&highlight=


As in the case of the OP, the longer you take to reply to a message, the greater chance you have of being logged out behind the scenes while typing, and thus losing that long and detailed reply you've created.