Hi,
As per your Issue, system is taking RETRO with out changing the salary amounts.
In addition to salary changes system will take RETRO whenever you will change the data of IT0000, 0001, 0007, 0008 and IT0027 these records with previous dates system will take TETRO. Kindly check these Info typerecords also.
If you don't want RETRO for any employee you can restrict in IT0003 field "Earl.pers. RA date",
In this field if you will maintain 01.07.2015 system will generate payroll process from Jukly month on wards only beyond the date system will not generate PY run.
Regards,
Venkat Polisetty