When training the Avatar at the List field in Monitor, any party member wearing an invisibility ring will completely disappear (instead of being "greyed out") and is dumped from the party
This occurs when the pikeman asks "What weapon dost thou favour?" (After the trainer says "I will train thee now")
The dumped party member/s though completely invisible stand in the same spot - you can double-click them and have them rejoin the party.
Save game attached.