Fixed value date field in invoice

Hi Friends,

I am creating contract then sales order then invoice.And for mainating price thro' VK11 for combination of sales org/DC/contract/material and entering valid from and valid to date in VK11. Now I can see that price in sales order and subsequent invoice. Now there is one field in invoice header fixed value date (VBRK-VALDT) that is showing as blank, that is correct becoz in VK11 fixed value date I have not maintained anything in field fixed value date.

Above scenario I tested in dvelopment in development and got the result as mentioned above. Now when I check one invoice in production found that there is one entrey in VBRK-VALDT field as 01/01/2010 but when I checked VK13 then for combination of sales org/DC/contract/material and found that there is no entry in fixed valuedate in VK11 so from where the value is coming in VBRK-VALDT.

Now I created second contract and maintained the price thro' VK11 but now maintained one value say 01/01/2010 in fixed value date field in VK11 now I created the subsequent sales order and invoice and found that there is entry in VBRK-VALDT whatever I maintained in VK11 fixed value date.

So why problem is happening in production even though fixed value date is blank in VK13 there.

Any pointers

Regards

Ashu