I had a different though partly similar problem two weeks ago (latest patch 1.4.03). Saving the game was no problem. But whenever I pressed "advance turn", the game was saved instead and I was sent to the main menu. Reloading the game always yielded the same result.
Finally I solved it by restarting from an earlier savegame (I lost only four turns), which I had saved manually (copy-pasting the savegame files into another folder).
I don't know what the reason for my problem was, and remembered too late to have a look at the log files. They already had been overwritten. At least, after having re-started from the earlier savegame, the problem did not turn up again. Fingers crossed ;-)