If Current Navigation is not same as Parent Site Navigation...

If you set Current Navigation to “Display the same navigation items as the parent site” and if you don’t find the same navigation items as of the parent site, you might need to add an EnableInheritance="True" attribute to the

PublishingNavigation:PortalSiteMapDataSource as in this example:

SiteMapProvider="CurrentNavSiteMapProvider"
EnableViewState="true"
StartFromCurrentNode="true"
StartingNodeOffset="0"
ShowStartingNode="false"
TrimNonCurrentTypes="None"
EnableInheritance="True"/>