I am using Moodle 1.7, and I had the same problem that you have.
In order to solve it, I had to set more than 30 minutes between the "End of Sumissions" deadline and the time for the "Start of Asssessments".
I think that this has to do with the "maxeditingtime" variable, which is set to 30 minutes by default. When a student sends a message to a forum, it is really forwarded to the forum (or at least other students are notified of his submission) 30 minutes after he sends it. Something similar must be happening with the workshop, so that you need to set more than 30 minutes between those two phases.
I HOPE THIS MAY SOLVE YOUR PROBLEM.
see the original post at :