None of this should explain why your game is not being saved. It shouldn't matter -- the save game function should work in spite of having not done anything, so I suspect this is a bug.
Exactly.
Actually, I already noticed this load/save problem a few days ago when I was actually playing the game and making turns. Today I just started the game and quickly grabbed the relevant screenshots without actually playing the game and taking turns. But as you said, this shouldn't matter, saving doesn't depend on having to take turns, you can save anytime, obviously, so not making turns cannot be the cause of the problem (and the autosave interval is set to every two turns).
What I don't understand is that if this is indeed a bug, then why aren't the others experiencing this as well? As far as I know, nobody else has reported it. What is different?