[iaen]

I've had this happen a few times as well, although I mostly had problems getting the log window back in front of the main game window... I've never found a really reliable way to get the windows sorted out properly. Sometimes after you Alt+Tab a few times or select the game in the taskbar it works again, sometimes it doesn't.
It's happened enough times that I automatically disable the 'display log on turn start' when I'm going to switch back and forth a lot. Haven't had any problems since.
I also always use autosave on every turn ever since I first ran into this.