Balance Field "Profit Center" not filled

Dear All,

I have created a Po with subcontracting item category L and Account assignment M. I successfully completed MIGO. While creating MIRO, I enter all the details, calculate tax and when I simulate, I see an extra G/L account being determined. This account is for Subcontracting Charges.

My questions:

1. Before we use to create Po of subcontracting item category L without Account assignment M, during MIRO the extra G/L account of subcontracting was not determined. Only there was an account of GR/IR Clearing A/C.

2. Why is it getting determined?

3. Can I assign Profit center to G/L Account.