Mathieu,
I'm using #23165 snapshot, I have 4 MDs, 2 of them were OK and 2 did not have the "Media Scenario" even deleting the MD and recreating them today did not work, so I looked into the "My Scenarios" from WebAdmin and found 2 rooms had duplicates so I went to the 2 MDs that didn't have "Media Scenario" and changed them to a new room and reload/Regenrate All, then I've got all MDs with all Scenarios.