Is there a way to modify sequence of journal entries ?

My problem is that i'm trying to enter 2012 accounting. I modified invoice sequence for customers and suppliers (replacing %(year)s by 2012) which now looks like Invoice AM/2012/0084 so this part is ok.

The problem is that when an invoice is validated and paid, the journal items corresponding have a journal entry number corresponding to 2013, eg AM/2013/0002, even if the period and the effective date correspond to 2012.

How to change this behaviour in v7 ?