Parallels Plesk Panel version 11 has its own PHP selection functionality.
More information you can find here.
It is fully compatible with our PHP Selector and CageFS. What happens is that Plesk selector switches 'native' PHP version, while our PHP-Selector switches site to alternate PHP versions.
If you install different PHP versions from the link above to activate it for the customer you are required to run:
# cagefsctl --force-update
Resellers have no control over PHP-Selector, and shouldn't have any. Only admin & end customers have control over PHP-Selector.