http://www.bbc.co.uk/dna/mbarchers/NF2693943?thread=7851583&skip=0

threads from this site, such as this page, seem to randomly have the left
panel that gives the list of message boards, missing.

It happens often enough that if you try downloading a few threads a few times
then it will happen that the panel will be missing in one or more of the
files.

So a possible bug.