Can't do anything after loading multiplayer save

[No. 2 Bunger]

As in title---playing vanilla BtS on Steam with friends, the first multiplayer session went fine, but the next week when we loaded the saved game, we found that I (the host) could not move any units or end turn, so that game was stuck waiting for me to end turn. This occurs even if I load the save in an MP game in which I am the only human player. Is this a known issue with any fix? So far the only thing we've come up with is starting a new game and hoping it doesn't happen again.