- Have a Promoted Seliph Dismount, then wait.
- Have a Dancer Dance to give him another action.
- Have Seliph take another action
When these actions occur, Seliph will be greyed out on all of the turns after the glitch is triggered as if he had already performed an action that turn. Another oddity is that instead of the cursor returning to Seliph at the beginning of your turn, it starts in the top left corner of the map. You can have a Dancer Dance next to the bugged Seliph to allow him to continue through the map, but if you finish the entire Chapter and move onto the next, Seliph will disappear entirely and is absent in the throne room, thus making it impossible for the game to be finished.
There are rumors that dismounting with Seliph by itself can be unsafe, though the people reporting this may have been accidentally triggering the glitch and not understanding how it happened. The steps above will consistently trigger the glitch every time.