If you’ve configured path based exclusions in FCS 1.0, you may notice that mount points in the path tree are still scanned. This happens because the mount point resides on a different volume than the parent folder. When a file is accessed on the mount point, FCS receives a device path that is not a child of the excluded folder and FCS doesn’t connect the mount point association when it applies the exclusion.
This is a known issue, and we apologize for any inconvenience that this might cause.
Chris Kemper, Senior Support Escalation Engineer - MSFT