folder permission Windows Server 2008 R2

I'm having a bit of trouble setting a special folder permission in a folder.  This is a single Special folder among about a hundred client folders.  This particular "Special" folder is a client folder for one of our employees, so I would like to make it accessible only to the four necessary people in our "Principals" group instead of the 15 people in the "Our Staff" group.
I have removed "Our Staff" and added "Principals", even set the folder not to inherit permissions from the Clients folder which shares to the "our Staff" group.  
Effective permissions say that only the four people in the Principals group should have Full Control and permissions of any kind are unchecked and greyed out for any other user that I check under effective permissions.
Problem: when I navigate to the folder when logged in as an "Our Staff" user, I still have full control access to the files/folders in the Special folder.
I guess I'm looking for a checklist of things I may have not taken into consideration or have done wrong when sharing?  I just don't get it.  Shouldn't this be the most simple thing?!
Jarrod AdamsconsultantAsked:
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Toni UranjekConsultant/TrainerCommented:
Post pictures of ACL editor for share and NTFS permissions. Remove sensitive data from pictures.
David Johnson, CD, MVPOwnerCommented:
did you remember to check the box to apply these permissions to all objects when changing the permissions (the bottom checkbox)

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Jarrod AdamsconsultantAuthor Commented:
Any idea what the "System" group is?  It is showing in the security box as a full control, but I didn't add it specifically.
David Johnson, CD, MVPOwnerCommented:
System is the computer it has the highest privileges.
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Windows Server 2008

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