When a file was checked in 2 different times (for example: artifact was checked in here and merged to trunk at and a second time here we can end up with a wrong timeline, like this:

In that timeline, there is a fork in the trunk based at ec81aee915, while in fact the correct sequence of events was that the same file was checked in again between the two "heads" of the trunk (at 77f53423ae).
Both the second checkin of the file and the linearity of the trunk timeline are missing from that page.