there seem to be a few posts related to this issue, e.g.http://forum.linuxmint.com/viewtopic.php?f=208&t=113446http://forum.linuxmint.com/viewtopic.php?f=208&t=103320
I'm suffering from that feature, too. I work a lot with VMware in unity mode and windows applications running under wine/cxoffice. Pop-ups and tooltips often leave behind those described artifacts on the desktop. I had the problem under Cinnamon 1.4 and hoped to get it fixed with 1.6. However in 1.6.1 it still exists. I have gnome-shell and unity installed in parallel and neither show the described effect.
This is runninr Mint13 on a Dell Lat E6230 with an Ivybridge integrated graphics card.
These artifacts render Cinnamon rather unusable (pity!) for me at the moment since having to restart via ALT-F2 "r" frequently is annoying and a disturbing interruption of me work.
Please let me know if I can provide any information or test to help getting the issue solved.