In the presence of an error or simply when interrupted, $out cleans-up after itself in its destructor. If the output of $out was to a timeseries collection and the interrupt happened after the temporary rename, then it has to drop the buckets collection. This code assumes that the collection it is dropping is the same it created. However, between the rename and the drop the collection could've been dropped and re-created, thus it would be dropping an unrelated collection, leading to data loss. The goal of this ticket is to fix this race condition, perhaps by dropping specifying the original UUID.