Funds Management. Commitment item getting reverse when posting an IR

Dear gurus, this is our scenario:

1) We create a PR based on GL Account and Cost Center. When we save the PR, FM shows the amount revserved for this PR.

2) We create a PO based on the above and again, FM is working fine, showing now the amount that was reserved for the PR, now reserved for the PO.

3) We do the GR and everything is correct just as the two steps above.

4) We do the IR ((using MIRO), and now the commitment item does not show anything at all. In fact the amount is reversed and it looks like there was no budget consumption.

If we do a MR8M to reverse the invoice, then we can see again the amount in the commitment item reserved for the PO.

We only have this issue with IR (MIRO) when we post an invoice using FB60, the system is working correctly.

Any help will be rewarded.

Thanks!.