Map: Random encounter during rest while traveling (High priest, acolyte and a few veterans)
How did it happen: Cast "Dominate Person" on an enemy character (specifically the high priest in this case) and have them survive the encounter. Then click the fireplace to continue travel. The character will show up as a follower (a 5th icon in the party portraits during travel, see screenshot: screenshot ). Then the dominate person timer should elapse before another encounter/destination.
If another random encounter then happens while traveling, the encounter loads but a black screen appears and nothing can be done.
If the party reaches a destination, the character spawns next to the party and appears as a follower party member, but cannot be controlled: (Screenshot: screenshot) They can be attacked (with a spell, don't know about weapon attacks), but doing so doesn't start a battle, but makes the UI disappear. Characters are controllable and movable but moving to the area transition rectangle (in the above screenshot) doesn't do anything.
When did the save happen: Fresh run, bought the game and started the run on the day of release.
Save games: I'm sending two save games to the save game email, one is pre-travel (same as the first screenshot), and one is after arriving to a destination (the second screenshot). Loading the first and traveling recreates the bug. Loading the second and attacking the extra character recreates the loss of UI.
Hope this helps. This is an amazingly wonderful game and I'm so glad I bought it. Keep up the amazing work and hope more content is coming!