Decks disappearing from playback logs? Not a mask issue

I’ve been developing a Mage Knight module (fairly recent builds up at … Board_Game)

Everything always works fine solo, and most play-by-email games have also gone flawlessly. I haven’t tried server play.

The problem occurs very occasionally when a player is playing back a log file created by the previous player in which decks were shuffled - especially when the ‘dawn/dusk’ global shuffle is triggered. All the decks (in one case all decks bar the player who did the shuffling) disappear, or in one case only one card was left face up in each player’s ‘always face down’ deck.

This variety of bug effects and the inconsistent trigger conditions have left me completely baffled as to the cause. Does anyone have any insights to help me sort this out?