Billing Posted in Next month accounting document in Current Date

Hi Friends,

I am facing problem while creating invoice, it  is getting posted in next month and accounting posting date is posted in current date. This problem happens rarely between 1000s of invoices and in last week of months.  Always i get a single case in each month end. If i tried again that with cancel billing and create again the scenario is not getting replicated.

For Ex. After PGI in date 27.08.2013 i created invoice the invoice is getting posted on 01.09.2013 and accounting document posted in current date 27.08.2013.

I am also not able to get same scenario. Please provide your valuable inputs on this scenario.

Thanks

Deependra