With a bit more testing I found that on starting the Queue Manager will restart the last incomplete render. Even if this render was cancelled. This happens even after the render has been removed from the queue. Since I have a problem when renders crashing this even happens if the render was reported as finished (after a crash) but it actually was incomplete.

The last incomplete render job just shows up as an entry and shows running with an increasing percentage complete.

In my opinion the entire Queue Manager is not really a well though out product. It could have been a lot better when implemented as a real queue manager comparable to other queue managers.