Sorting criteria not validating in Z Programe development

We are in process of data fatching in a Z development program and faced with following situation;

1. We pass criteria as Fiscal Year 2010 and posting date as 01.04.2010 to 30.04.2010

2. Accourding to above input we fatch data in MSEG table

3. But when passing the MSEG reference field into header table MKPF we find different date (i.e. October 2010) which is different from initial data range (i.e. April 2010)

It seems that we are unable to put date check criteria,

How could we initiate the date check successfully. Kindly suggest.

Regards

Mayoor