How are you removing rights? Are you doing it through the NWADMIN program or Windows Explorer? I simulated step-by-step what you did. Due to how my network is configured all my users had access to the folders as well. I went into the Windows Explorer and there were no rights assigned to the folder. I then went into NWADMIN and assigned Specific rights to the folder and removed all the Inherited rights (with the exception of Supervisor because that should not be removed) When I went to the folder again, only members of that group had access to it. Now if you only wanted supervisor access, you should be able to remove all rights from Access Rights and the Inheritance filter and only supervisors should have rights to it.
Since I am sure our networks are completely different as far as rights go I don't know how much use this will be to you. The good thing is that I was able to simulate your issue and hopefully give you steps to check. Let me know if this helps you out any. If you need I can send you screen shots of what I'm doing. If you're not already, remember you always have more control using NWADMIN then Windows Explorer.
david e
there are just some end-users that need reBOOTing!!!!!