Time machine not performing housekeeping - previous days' & weeks' multiple backups remaining
As you can see from this image, time machine stopped cleaning backups from previous days and weeks.
A bit of background, this is a networked backup for a MacBook Pro. (Thus, the backups only happen when I'm at home on my home network.) The MBP: OS 10.8.4 2.4 GHz, 8 Gb: 750 Gb drive, currently using 125 Gb - 625 Gb free.
The time machine "drive" is a 350 Gb partition on a 1 Tb drive, 75 Gb free; the other parition has the time machine backup for another MBP, also OS X 10.8.4; this problem does not occur on that time machine partition with that computer. The problem started on 5/12 with previous days multiple entries not being deleted. (The timing does not seem to align with a software update: 10.8.3 on 3/25 and 10.8.4 on 6/6.)
One more thing, backups take much longer (around 25 minutes for just a few Mbs) than they do on the other MBP which uses the other partition. The other MBP has many more files and folders and the .sparsebundle is bigger (252 Gb).
I have read through Pondini's wonderfully thorough website on time machine (pondini.org) and looked through discussions here. All seem to focus on ways in which time machine prunes old backups to make space. In my case, space is not (yet) a problem, but I am concerned that these problems indicate time machine is not working properly and that there may be other problems.
MacBook Pro, OS X Mountain Lion (10.8.4), 8 Gb memory 750 Gb disc