AP invoice cancellatio event in Adjustment period

Hi,

I have the following situation in production: (R12)

The Subledger Period close report shows that an AP invoice with the event type as invoice cancelled is in Adjustment period. My invoice is in Dec-11 period, cancellation is showing in DEC ADJ period. The adjustment period is closed in GL and DEC-11 and JAN-12 both are open. If I run create accounting program, where will the entry be accounted since adjustment period is closed in GL? ALso, if someone can shed light on how this could've happened, it'll be helpful to avoid in future.

Regards

Meenakshi