PR Some lines returned and create mins encumbrance

 Dear Team,

We have approved PR  in Oct-12 with 10 lines Amount $ 100,000  and auto created a PO for  line # 01 amount $ 90,000 in 31-Jan-12

Before Auto Creating PO we have returned PR lines # 2 - 10.

Now, PO has created and Obligation Amount $ 90,000

But, in the PR Returned lines # 2-10 which created mins commitment $ 70,000. (which equal  to line # 2-10)

Now , We can  see in the budgetary inquiry window Commitment as $ -70,000  and Obligation as $ 90,000.

How this $ -70,000 commitment will nullify ?

What is exactly mean by returned PR.

Year end encumbrance carry forward not yet..

Version 12.1.3

Please clarify

Thanks