Here is a screen shot of bug we have, both users on .8941 engine. This is a saved game
@adamf Did you take a history savegame (a beta feature, in that you right click history to get the savegame)?
@adamf Not sure, but updating game engine to most recent is always a good idea when strange errors pop up. Here's a link to latest version.
If that doesn't help, post the save game file too.