Page Not Blocked Until I Hit "Back"??

I use NIS 2010 with Firefox 3.5.

 

Recently I was on a page of a site I trust.  I clicked on a link to get to a "contact us" page, and then clcked on a "maito" link that opened an Outlook email template, and I sent an email.  Then I clicked "back" to return to the previous page and NIS instead flashed a warning that the page I was trying to go to was suspicious and would not return to it until I gave permission (which it said was not recommended unless I trusted the site).  I did choose to return to the page.

 

If the page was suspicious, why didn't NIS give me the warning the first time I opened it -- only when I tried to navigate back to it less than a minute later?  I'm pretty sure the url was the same each time.  In my history I see that the Symantec warning page url has the term "suspiciousredirect" in it.

 

Any ideas appreciated.

 

EDIT:  A secondary, related question:  The help file says that the Miscellaneous Settings has a way to disable automatic threat submission.  But I can't find any such option.  I probably wouldn't disable it anyway, but where is the option?  All I see is an option to disable Community Watch.

Message Edited by Ardmore on 01-03-2010 04:40 PM