I use Mint 13 with Gnome Shell 3.4 . For the last month or two I have had an issue that randomly occurs, and once it does only logging out or rebooting fixes it.
I randomly have a problem that causes at least these things:
1) Right clicking on icons does not work, if I do it acts as if I have right clicked on the desktop
2) In Google Chrome if I right click on a page to open a link in a new tab, if I go back to the original tab it is no longer functional until I reload the page.
3) When I am in a text editor (even in a Virtual Box system,) and click in the editor panel, it acts as if I was holding the shift key and highlights the text from where the cursor was to where I clicked.
My first thought was that this is a keyboard issue so I opened up Wire Shark and there is no input form my keyboard. I have searched around but have not been able to come up with a fix.
Let me know if you need any more info.