I'm hoping some geeks might be able to help identify the cause of an annoying problem I am having with Facebook. The problem is that I don't receive basic notifications when somebody comments on my posts.

This picture is an example. As you can see, about an hour ago somebody (Jade) commented on the link I posted. I was surprised to see it, because I received no notification of it, as shown in the top part of the photo.
Even when going to the separate notifications page, there is no record of the comment:

This has been going on for a month or so now - I used to receive notifications without problem - and it's not every comment notification but it is most of them. Oddly enough, "like" notifications always come through.
Facebook has a notifications settings page, but here you can only enable or disable email and SMS notifications. I assume that the normal notifications (that I'm not getting) cannot be disabled? Or am I missing something? Are there other settings I may have changed by accident?
I am using Firefox 4 and have tried clearing my cookies. I might try using IE for a couple of days and see if it still causes the problem.
I have also tried to contact facebook, but they don't reply to people, you just get a "thanks for reporting this issue" automated email.
Another thought is that my ISP uses an akamai server to cache facebook... this wouldn't be the cause of the problem, would it? Coincidentally, I changed to this new ISP (snap) about the same time.
Any other ideas? This is frustrating the hell out of me.
Thanks :D
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