Not able to extend rule which is not in the same package in BPMS 6

Issue

We have a rule named "Rule1" in package 'com.sample'. Another rule named "Rule2" in package com.sample.gss'. We want that rule "Rule2" will extend rule "Rule1".
Rule "Rule1" does not appear in the list of "EXTENDS" when I edit rule "Rule2". If we try to extend rule it faile with below exception:

Unable to resolve parent rule, please check that both rules are in the same package