I had the same problem and finally tracked it down to a new feature they added to Parallels 8 called "KeyboardLayoutSync"
It is supposed to sync your Windows keyboard to MAC but seems to screw up my Apple English International keyboard instead.
You can switch the feature off like this:
1. Shut down virtual machine
2. Location virtual machine file in finder
3. Right click and choose 'Show package contents'
4. Locate and open the config.pvs file with textpad.
5. Find the key: KeyboardLayoutSync
6. Set the value to: 0
7. Save the config file
Open Virtual machine and VoilÃ - problem fixed.
For the Apple English International Keyboard, use the following language layout in windows:
"United States ISO/RU (Apple) - Parallels"
Last edited: Apr 12, 2013