Analysis Services Security: Multiple Roles in Tabular vs. Multidimensional

In terms of security tabular and multidimensional models of SQL Server Analysis Services are very similar. Both use Roles to handle specific security settings. Those Roles are then assigned to users and groups. This is very trivial if a user only belongs to one Role - the user is allowed to see what is specified in the Role. But it can become very tricky if a user belongs to more than one role.