Duplicacy of GR(mvt 103) wrt. Outbound delivery

Hi,

I have created an intercompany STO with 100 qty, after that do delivery(VL10B)) then PGI(VL02N) and then GR(MIGO with Mvt.:- 103) with 5 qty wrt. outbound delivery. After that when I posted again GR of 5 qty without creating delivery and PGI , system is allowed and posted.

Why system posted two GR, however delivery and PGI was done only once.

Regards

Jayesh