while doing back date entry in a/p ,Je is picking current fy series

Hi

We are Making A/P invoice on 31.3.2013 with FY1213, for which JE is also created using same posting date i.e.31.03.2013.But JE is picking current FY series which is 1314.

where for je last year numbering series is unlock and financial of fy1213 is unlock.

what we have noticed is for je document fy1314 series is default.

Kindly let us know what can be reason for same.or it is sap b1 standard functionality.if yes kindly share sap document if available.

Regards

Ashish