custom PHP version not showing with nginX

[ethanielc]

Environment : Centos 6 + Plesk 12.0.18

Installed PHP 5.6 co-exist with current 5.4. I realize domain/sub-domain with 'Process PHP by nginx' enabled not able to select custom PHP version 5.6 is not in the list.

With the option disabled i can select custom PHP build. Is this correct behavior?

Thanks!
FuLin.