Blackberry Desktop Manager -> Synchronize -> Configuration tab -> Config synch... -> Tasks -> Configure -> Advanced Settings... -> Field Mapping: Now set the handheld "Start date" to NOT synchronize.
Why does this solve the problem?
On the blackberry, tasks don't have a start date. My guess is that Intellisync is finding a number it thinks is a start date, and that number is being converted into a strange start date in Outlook. In Outlook, whenever a start date is AFTER the due date, the due date is set to be the same as the start date.
Here is the source
"Simplicity is the ultimate sophistication" ~Leonardo Da Vinci