Attached save and a nice screenshot to boot.
Don't envy you debugging that one. :)
Plain A3.410, no mods.
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your save names are excellent.
Vanilla RimWorld or were you using mods? If using mods, which ones, and in what order were they activated?
Vanilla. Edited, thanks. :)
This should be interesting to figure out. No promises. :)
EDIT: Fixed save attached below.
The two faction squads that were present when that game was saved have been removed. The problem was caused by one of them.
Thank-you for providing the save. It will help us find the exact cause of the bug, and hopefully lead to a fix that will prevent it from occurring in the future.
The problem is caused by loading a save that has pawns from a friendly faction providing military assistance present in the world.
A workaround until this is fixed is to save the game prior to calling another faction for military assistance, or to save after they have left.
EDIT3: Definitely a bug. Reported on Mantis (http://ludeon.com/mantis/view.php?id=689).
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Were you using the hotkeys in the architect to build something at the time? Or is this from loading up a save game?
Thanks for making it proper. :)