Dasty, if you look around further, you will find a thread addressing why this happened. Essentially, the AI tries to intelligently decide who to hire for battles. Who they hire is based on past performance in strat battles and most likely level. In addition, they also take into account recent activity. If a person is not active on the website or game before a battle, they may be kicked.
The list is constantly re-prioritized based on whatever criteria they use, so it is not a bug.