It's most likely caused by having a '-' (dash) in the name of your station in WD, Control Panel, Web Files/Web Page, Real Time Client FTP TAB,
Your weather station name to appear in the client viewer
The '-' is used as a separator in clientraw.txt for the 'name_of_station-hh:mm:ss' field, so just take any '-' (dash) out of that name and the AJAX updates should appear with the correct time (and the seconds ago counter should reset normally)
Best regards,
Ken