I just noticed that when I thanked someone for their edit on my own talk page, the value for logging.log_page field was 0, rather than the page ID of my talk page. This is bad behavior; the correct page ID should be logged.
A quick look at the database shows that 0 is in fact the most common page id with log_type = 'thanks' which means a lot of the log_page information logged by thanks is junk.
I think this should be fixed in two parts: (a) the correct page id is always logged, never a 0, and (b) the update script will find the page id for previous thank events and replace 0 with correct id to the best of its ability.