Incorrect Pur grp determined in PDP scenario

Dear All

Please advise  I am trying to setup a PDP scenario and when in the PR and the SC different pur org are being picked up Please could you explain the reason for the behavior ?

For example : I maintained in ECC pR pur grp as 100 and in the SRM it is picking up a random Pur group as P12

I also checked this has got nothing to do with Category ID as in the product responsibility it says product category as asterix for both .

Also I have assigned the RFC user under the root org structure 

Please could some one help me understand how to ensure the Pur grp should be the same
Any help would be much appreciated .

Regards

Vinita