Coincidentally we encountered the same issue as the OP on the same day, so we as well have tried the proposed solution.
The only thing that we have noticed that it took us up to three tries to delete all objects.
In other words, during the first try we got an rc of -3 on some of the objects and on most of the objects an rc of 0.
During the second try we had an rc of 0 on the remaining objects but one. The third try removed the final one.