Sorry if this is in the wrong place, I never know where to post this type of thing.[phpBB Debug] PHP Notice: in file [ROOT]/viewforum.php on line 474: Undefined index: mark_time

EDIT: An update. If I go to 'Load settings' and find '
Enable server-side topic marking:
' and set it to 'No', that's when the debug message appears. If I set it to 'Yes, then the debug message is no longer there.What gives?