EDIT: I notice that there are .sav files in my directory for each of the missions I tried. I thought Ares had save/load disabled?
It has save-load disabled during ingame. The saving-at-mission-start code isn't skipped tho, but even those saves are broken.
Happy holidays,
I've had the chance to try MO3 at the weekend using a Windows 7 PC and I can confirm that the same directory (literally the exact same folder) works perfectly fine, with no issues restarting missions. It seems to be a Windows 8 specific issue, though I can't for the life of me begin to explain why.
I've tried all sorts of compatability settings and colour reduction modes, but it just doesn't seem to want to work. I won't have access to that PC for another few weeks, but I thought it'd be worth reporting in just to share my findings.