UM 4 has the option “Remove all” for logs. It can be used to delete all logs at the time.
In version 3 if you deleted a log, a backup was created for it - so you could make an “undo” and restore that log. That means, the space was actually cleared only either after a reboot, or when undo history was cleared (tool user-manager history remove [f]).
I suppose no one is interested in “undo” operation for log deletion. So next release of User Manager package (version 3) will make no backups of deleted logs. And those, who delete logs will not have the problems you described above. We apologize for the problems you had because of this undo “feature/bug”!