Why are my users seeing a hidden thread?
 

Why can some of my users see a thread that is hidden?

I went to ACP>Forums & Moderators>Selected the Thread and pulled down for Edit>Go

Under "Posting Option", I selected NO, for:
Forum is Active (Will not appear if set to no, but remains accessible if the forum's URL is known)

The tread cannot be seen by any of my users except for 2. How are these two able to see it if it was selected to NO. Why isn't this selection working for them? The only thing I found wierd is they say they are using MAC's.