Why can anonymous users see my block, whose visibility is set to hide it for anonymous users? I have a block on one of my sites, in which all content is private.  Anonymous users don't see any of my content types, any of my views, blocks, etc.

The problem is one single block.  The problem block is the only one not created by a view or a module.  I created it simply by adding it via the block page interface.  I have set its visibility settings to be restricted to a certain role (not 'Anonymous', of course :-)).

However, this is the one piece of content that is still showing up on my site for anonymous users (before one logs in).  I've cleared cache multiple times, so that isn't the issue.

Has anyone else run into this issue?  Why would the block not respect the visibility settings?  I'm wondering if there are some modules that may be interfering with this or if there's another explanation I'm not seeing....
The strangest thing fixed my issue.  I'm still not sure why.

I was placing the block in a certain region with the 'Context' module.  When I removed the block placement from that context and set it directly in the block's configuration page, the block stopped being visible to anonymous users.

Not sure why that would matter!  Placing blocks generated by views with the 'Context' module is not interfering with their visibility settings, but for some reason it was interfering with this one.  It's just a regular block with text, nothing funky.

In any case, that's what solved my problem...