These are no "starred" messages. The real "stars" are located in the extreme left column on your screen shot. The little yellow rhomboid stars signify that these messages are new (newly downloaded) messages. If you restart Tb the same messages will loose their star and will be displayed as "unread" (green point)

Thanks. Bit pointless!

Thanks. Bit pointless!

Unless you are interested in having to software identify the new email it has not shown you before. It is something I personally value as I have Thousands of unread messages almost every folder. Unread mean I did not read it. The yellow star means I have not had to opportunity to read it until now it is that new. A similar flag shows in the folder pane for folders with new unseen email in them as well as the folder going blue.