Website gets blocked by webfilterproxyd even without website restriction

Question

I have a Mac Mini running Mac OS X 10.6.4 which has Parental Controls enabled for an account, but with Website Restrictions set to 'Allow unrestricted access to websites'.

However, there is one website (which I cannot specify for confidentiality reasons) which does not load at all. Instead I get the following error message in the system log every time I try to access the website:

sandboxd[12606] <Notice>: webfilterproxyd(712) deny network-inbound 10.1.1.3:49757

Obviously 10.1.1.3 is the machine's IP address and 49757 in this case would be the port that the request was sent from.

The website in question is in no way a bad/inappropriate/illegal website, so I don't see why it would be filtered.

Disabling Parental Controls completely for this account fixes the problem, but I'd rather not do that.

Any idea how I can fix this, or why it is happening in the first place?