Seems like several mixes the history on the topic and board, but it could be that the history on the board is the real culprit. On the boards history there is an additional entry for "topic" which just link to the whole topic. This entry is a little out of context among other entries users has learn to expect to be about diffs. Usually the two first diffs is not clickable and only the complete topic is available. The entry for "prev" should always have a context for previous entry in the thread, as this would be more obvious and more readily understandable. The destination page for this link should also have navigational help for navigation within this topic.

The "cur" entry should also have a proper link target. This entry is important to get up to date on all new additions within a topic.

The entry "topic" should perhaps be whats now is "commented", and commented should not be linked at all. That link seems to be confusing. If an user follows "topic" into a topic, then there should be navigational help to find the next reply. This is especially important with the present ordering of posts, which together with the increasing coarsity of the dtg makes it very difficult to follow the actual thread. That is you mus go back to the history to understand the post ordering.