I also have this issue with Mint 12 KDE.
For me the software manager actually start, but then it looks like it close it self after the software icon list is shown. So, no time actually do anything there.
Also the update and upgrade did not affect this. No errors while update && upgrading. Some xorg got few updates. Also no updates waiting in mints update manager.
I how ever have no real issues with this, because Mint KDE is on in my test computer where I just check out different distributions, not in actual use.
But I just report here that same issue here.
Asus P7P55D, i5 750 2.6Ghz, 4GB DDR3, radeon 6540 (Gallium 0.4), 80GB Intel SSD, Dell 1920x1200, Dual boot, Linux Mint 14 Cinnamon, Windows 7