The View Advert Logs function by default looks at the destination location for the log file to display - if it can't find the file for the date you have specified though then it looks in the source location instead.The window defaults to tomorrows date and usually won't find the actual log for tomorrow yet because STS only copies it in when it needs it - i.e. after the last advert break in the current day.
Therefore typically for today and previous days it will show the one in the destination location, but for tomorrow and future days it will show from the source location instead.