I'll just dive straight in: after upgrading one of the packages from the "3" category ("not tested but believed to be safe") I noticed that every time I open a new window and maximize it, I get the black stripe all along its bottom border. Take a look here:
Now, when I un-maximize and maximize again, it doesn't happen i.e. it only affects the first maximizing.
Interestingly enough, the same happened on my Mint 11 which I use at work, so I doubt it's graphic driver specific (I got NVidia GeForce 9300M G/PCI/SSE2 at home and something from Intel at work), unless this issue affects both Intel and Nvidia.
Unfortunately, I don't know which package is exactly responsible for that glitch, since I fresh-installed both home and work systems about a month ago, so all the updates have been performed in a bulk.
I'd be grateful for any hints, because it's really annoying.