Maybe this problem was reported somewhere, but that's what I get. Everything saves just fine, but when I'm trying to overwrite existing savegame, process never stops: saving logo (with rotating circle) appears on screen, but never disappears. I waited for half an hour, but it didn't stopped. I hear music but the game isn't responding. The only way was to kill process via Ctrl+Alt+Del.
I expect it was just your fourth or so save in one play session? Including autosaves.
Double-checked everything. It seems you are right, this thing happens on my fourth saving (counting autosaves and quicksaves).