Websense thinks it is blocking HTTPS sites, but users can still get to web page

We use Websense Web Filter 7.5 build:20100417_1368 with a Sonicwall.

Usually, if a student tries to get to facebook/social networking sites via HTTPS (ie https://www.facebook.com), Websense blocks the request.  The student doesn't see a custom block page, but that's fine.  At least the page is blocked.

I noticed yesterday that the students can again get to social networking sites via HTTPS.   I'm not sure when this behavior began.  I test HTTPS sites periodically to ensure that they are being blocked, but I don't remember the last time I checked.  It's probably been a month or two.

So ... I ran testlogserver.  Websense thinks that it is blocking the webpage -- I see the following entry in the log:

protocol=    "HTTPS"
url=         "HTTPS://199.59.150.39:443"
port=        "443"
category=    117    (SOCIAL NETWORKING)
disposition= 1025   (Category Blocked)

But, after 10 or so seconds, the web page actually loads.  This happens in both Chrome and IE. 

I'm not sure where to start troubleshooting this.  What could be letting the request through?  What should I be looking at?

Thanks!
Jamie