same phenomenon here...
game loads ok, can start new games, can load old savegame of the "milkyway" map (which is little bit more than 4 times the size of the standard campaign savegame file)...
but trying to load an old save of the standard campaign (just 1-2 days before installing latest patch 1.2) scenario "contingency" the game is stuck at the "loading" screen (animated galaxy swirl) seemingly forever (several minutes) where the "milkyway" save loads in half a minute at worst -- oh, and the described workaround did it for me, too (pressing enter & space a few times).
interestingly if I immediately save that game again, without doing anything, the new savegame is smaller (4194k instead of 4228k) -- but it still has the same problem... loading never finishes without using the keyboard (space/enter, didn't try other keys ...).
sorry but I will be offline several weeks and thus unable to help with debugging, starting day after tomorrow...
so if you want me to upload those savegames for example, or anything else... tell me now 