VIN -
My install sends RR73 as the Tx4 message, and it terminates the automated contact sequence upon receiving 73 from my contact. 
Are you sure you are using the messages preloaded into tab #1, rather than tab 2 or 3? 
Whoops!  Apologies, I hadn't seen Neil's message just above mine.  Just click the Tx4 tab to switch back. 
 
Karl  WA8NVW  OH
WA8NVW@...
in WSJTX@groups.io