Icons on thread titles

On the lists of threads there is the thread originator's name and icon (or initial) on the left, below the thread name, and on the right there is the name of the last person to contribute, accompanied by an icon which is sometimes the one used by the last contributor, and sometimes that of the original poster.

Entirely unimportant, but strange coding to bring that about.
I think if you choose a specific icon for the thread title - ie not your own avatar or a system-generated initial - that icon gets used. So eg in the track cycling list, the last-posted icon for the Champions League thread is the thread icon but on other pages it is the last poster's avatar or system-generated initial. Not a lot of people choose thread-specific icons, they just let the system run with their own avatar.