Time Machine - strange behavior while deleting old backups

Question

Not sure if this is the right place, because this is actually not on Time Capsule, but on a Time Machine on an external USB drive.
In any case, I searched the web for "time machine delete old backups" and found many discussions of various aspects of this task. My objective is to clean up a partition on a the external drive that I no longer use for active TM backups, but to retain a small set of backups in case I need to go back to them. The partition now has other uses and I need the space. My main TM backup is now on a separate Time Capsule.
So again my objective is not to remove all backups, but just most of them.
It appears that the well-discussed procedure is the following:
Go into Time Machine.
Select the Macintosh HD.
Go back to one of the oldest backups.
Click on the Gear > click Delete Backup.
This procedure will remove one Backup at a time, and it seems to take 5 - 10 minutes for each backup.
Here is what I noticed that was "strange":
You could delete a selected backup using the above procedure.
For the first selected backup so deleted, there is a confirmation dialog with a warning message that it is not undoable.
After clicking OK on the warning message, the display backs up to the "Present" backup, and the administrative password is requested.
After the administrative password is entered, the backup starts but control is passed back to the user interface, and another backup can be selected to be deleted.
However, after the second backup is selected and deleted, there is no warning dialog, and no request for the administrative password. At this point the user interface is busy and nothing more can be done until the backup delete is completed. Except that the Time Machine can be exited by first pressing Escape, then Cancel on the lower left of the screen.
If the time machine is exited, there is a Delete Backups progress dialog with a progress bar for each backup  so far requested. If the second backup was requested, as in the steps above, there would be two backups.
I discovered by playing around that either you had to wait within Time Machine for the deletion to complete, or alternatively exit Time Machine. While I was not sure what was going on, I kept starting one backup, then exiting Time Machine and re-entering Time Machine and requesting another delete operation. Each time after entering Time Machine, the warning/admin password sequence occurred and I was able to exit. And then immediately re-enter Time Machine and request another backup. Only by exiting and re-entering could another delete request be made.
When out of Time Machine, I thus saw the Delete Backups dialog with any number of concurrent "Delete One Backup" progress bars.
Because of the nature of the hard links used to indicate backups, I was wondering if these multiple delete operations could possibly be hung in a deadly embrace, so I decided to only do one at a time. Some further study to see if the multiple delete operations were all able to complete would be needed to know if this would be a good way to "queue up" multiple delete requests.
Bottom line: seems like kind of an odd implementation. Would be really nice if you could select many (say 30) individual backups and delete them all at once, rather than taking 5 - 10 minutes each. Again, this is because I am trying to reclaim disk space, but not delete all the backups from a Time Machine backup set that is not in active use.
Also, the method of "queuing up" backup delete requests is kind of odd, but seems to work, with the proviso that I have not yet confirmed that doing more than one at a time actually works.

Answer 1

Heinz-G?uenter Arnold wrote:
since the upgrade to SL it seem that Time Machine has problems to completely remove old backups completely. The "removed" backups do not show up in Time Machine anymore, but the backup folders and part of their contents can still be seen in Finder.
Hi, and welcome to the forums.
That happens occasionally, in both Leopard and Snow Leopard, sometimes after something was deleted from the Finder, but also after an abnormal shutdown or improper disconnection of the TM disk.
Run a +*Repair Disk+* on it via Disk Utility, in your Applications/Utilities folder. If it finds errors, but can't fix them all, run it again (and again) until it either fixes them all, or can't fix any more.