If a client accesses a non-existent database by reading it, a side-effect of that action is to cause listDatabases to believe in its existence. Further, listDatabases reports its sizeOnDisk as 1 byte, but sets the "empty" flag to true. This is confusing. Non-existent databases should not appear in listDatabases, even if someone attempted to read from it. Should they appear, they certainly shouldn't be reported as having a size on disk, when they have no associated files.