If I continually access the site, this doesn't happen.
If I go through the site, stop for a little and continue, it seems like my session has been reset.

What I do to get around this is go through all of my new posts and right click to bring up each thread in a new instance of explorer. Once I have up the 20-30 or so I then take the original back to the beginning and then review and/or respond to each thread. If I walk away and come back. I can see that my search pointer for new posts has been reset, but I have the other messages up so I can continue without a problem.

Just make sure your PC has enough memory to do this.