Edit: And fixed! Will be in the next patch.
That makes sense actually. A weird artifact of RPGMaker is that there's always a "map" suspended in the background when you're on the initial title screen, and when you return to said screen this map isn't cleared: it's only reset when you load a save, which I'm obviously not doing with the gallery. With picture-only scenes this is irrelevant, as you never see the map or have a chance to interact with it, but the tunnel setup brings all that out. Should be fairly simple to fix though: just reset things when the player uses the locker. Thanks for the report!