I can confirm this issue. Running the latest Mesa built from Pali's 12.04 backports PPA (https://launchpad.net/~pali/+archive/ubuntu/graphics-drivers) I am seeing the same kind of graphical corruption in tooltips: They will often look scrambled and, as pointed out above, are sometimes replaced by textures from other apps (e.g. my dock). As far as I can tell this is restricted to Chrome for now.