Time Capsule filling
I have a 2nd Gen 1 Tb Time Capsule, model A1302. It's sole purpose (in addition to being my main router) is to back up 3 machines: an mid 2010 MacBook Air, a mid 2012 MacBook Pro and a late 2006 iMac. All are running OS X Yosemite except the iMac which runs 10.5.8 (and is hardly ever on).
Recently, I started getting messages through TimeMachine on the MacBook Pro that the Time Capsule was full. Clicking Details told me that the Time Capsule had only 8 GB of space. This is nigh on impossible because the 3 machines have combined less than 500 Mb on all three hard drives. Also, the MacBook Air was still getting successful backups and has not been getting the Time Capsule is full message.
I tried looking at the Time Machine in Finder through the MacBook Pro, but nothing I could do in Finder would mount it (including setting Preferences to Show Connected Servers on Desktop). Finally, I ran Disk Utility on the MBP. Using that, I was able to see that the Time Machine had a stated capacity of 997 Gb, with only 9 Gb available. I ran a Verify and it indicated the Time Machine needed repairs. I ran Repair Disk and all the space was recovered. After Repair Disk, there was 562 Gb available. Time Machine then successful ran on the MacBook Pro. A total of 20 Gb was backed up.
24 hrs later, Time Machine on the MacBook Pro (and only the MBP) is once again indicating the Time Machine is full. Details said there was less than 2 Gb free. I once again ran Disk Utility on the MBP. When I opened Disk Utility, it showed only 8 Gb available. I skipped the Verify step and went straight to Repair Disk. After a few minutes, it reported no repair was needed, but the available space was once again at 582 Gb.
Why is Time Machine convinced that there's no space on the Time Capsule? What is causing it to fill up? How can Disk Utility recover space when nothing needs repair? And what can/should I do to stop Time Machine from running out of space?
MacBook Pro (13-inch Mid 2012), OS X Mavericks (10.9.4)