If it helps your troubleshooting: it seems that this problem occurs with some threads, but not all. It is consistently happening with the following sample threads:

Miles&Points > Hotel Deals > Daily Hotel Deals (Groupon-Voyage Privé-Bloomspot-etc)

Miles&Points > Mileage Run Deals > Mileage Run Discussion > Trick it / negotiate it / special savings lounge thread

When I click on go to last post for these threads, it takes me about a week back (despite reading daily and clicking "mark this forum as read").