Outlook 2007 Tasks and Blackberry Problem

I use Outlook 2007 at work with a Blackberry Bold.
But I have one big problem, if I mark a task complete on the Blackberry, it marks it complete on the Blackberry and in Outlook. However, the completed task just moves from the day I completed it to the next day, to the next, etc. You get the picture.

This is quite frustrating and I hope to get this solved. Are there any suggestions out there?