Hello Vijay,
Logic behind this statement is ,encashment date will be update with respect to check number in PAYR table when you upload statement through FF_5 or FF67 if you are using algorithm '013. If delete the statement ,PAYR data won't delete.
Same statement ,if you upload again system couldn't bring BELNR-GJAHR number with respect to assignment or check number from PAYR table to table FEBCL as SELVON. Your clearing always happens based on SELVON.
Regards
Mani Kumar