There's a glitch in the board. We're aware of it. It exists. It's currently just not a priority to get fixed since there's an easy way around it. Every so often, possibly when you've deleted your cookies or logged out of the board and back in on a different computer, your viewing options for threads will change, and you'll get a "collapsed" thread with just the first post visible, and every reply to the post in a nested, collapsed column.
All you have to do if this happens to you is click the "Options" dropdown button at the top of the the thread, and select "Standard" under "Display Modes."
That's all. If you have your cookies enabled, the problem should be fixed from then on.