Standard pay reverting back after importing

hi   Myob Team,    when i set  up a new employee, under  the STANDARD PAY  tab,  i  zero out the total  HOURS   for  may staff members, as we use  Time Sheets  and import  hours  into  MYOB. However , each  fortnight the hours are  duplictaed , as  the standard  pay tab the hours  go back to 76, althought  i  zero out  manytimes.   why  wont they stay as  ZERO  please ??

 

thank you, 

Stone