Just to add to your post. I am also having problems syncing tasks from Entourage.
When I change a due date on a task in Entourage and sync., the due date on the task on my BB is wiped out completely and the task goes to the bottom of the list as an undated item.
I applied your fix and it seems to be better but still not working 100%. Now, the date in Entourage seems to be updating on the BB record but if I updatew the BB record and sync., the date is not applied to Entourage and and the BB task revers back to the date in Entourage. Reminder dates don't work at all and never have.
I actually have a ticket open with Blackberry Support and have sent several sync log files for them to examine. Apparently, there are known issues with task sync. that they are working on.