Has the logic behind dimensional security on shared members changed?

Summary:

Security logic that we have always used in the past successfully doesn't work any longer

Content (please ensure you mask any confidential information):

In our organization dimension we have two main hierarchies that we use for planning and assign security on. We have our primary hierarchy where all zero level members are set to Never Share for storage. Then we have a Yr1 hierarchy where the parent levels are set to Never Share but 99% of the zero level members are shared from the primary. This second hierarchy is used for Plan year purposes to account for organization moves, etc. We give security to groups on both of the hierarchies so that a group can plan on the orgs