Hi,
I have placed my messages regarding scavange. However, I do not know if the problem you describe is somehow related to the problem I have placed in the other thread regarding scavange.
The maillog stops after scavange. As you describe, there must be some bug somewhere.
I have found a solution to my problem, which is related to maillog stopping after scavange.
May be yoou could see if you also have something like this on your servers and confirm, as well as my solution for your server on maillogging.