I have done some tests using ethereal to trace what's going on. The difference between tables shown/not shown seems to be in the cookie send in the http GET request.
The difference between tables shown or not shown is immediately clear in the first http reply (200 OK) from gc.com, Content-Length is much lower if tables are missing, so the difference seems to be caused by the GET request sent.
If cookie is not sent (not logged in), tables are shown correctly
If cookie is sent with userid and ASP.NET_SessionId, tables are shown correctly
If cookie is sent with only userid, tables are not shown.
These results match with the experience the problem only occurs if a cache page is requested through an external link.
I used GCRQZ5 for testing via this link.
Responses are coming from 66.150.167.149, which resolves back to www.geocaching.com, so there is no proof of proxies being used.
I have trace files available if Jeremy cs are interested. My location is Europe, The Netherlands and I am using ADSL for Internet access.
I hope this helps to find the problem.