For me I had to uninstall the PD8 using something like appzapper or appcleaner (http://www.macupdate.com/app/mac/25276/appcleaner) Then reinstalled and this worked for me. I wasn't able to fix it by re installing parallels tools.
A hotfix has been released to address this issue. If you are not automatically prompted to install the update, go to Parallels Desktop Menu - click Check for Updates... and install the fix.
This release was made available September 6, 2012.