This is a warning for those using TaxCut (a pretty good Macintosh Tax program) and possibly other installers and upgraders.

The TaxCut upgrade installer scans all connected disks looking for copies of the software to upgrade. This is going to become an increasing issue going forward not only because of how big some of our hard drives are getting, but more importantly because of TimeMachine's appearance to other programs of copies of your entire disk (multiple times) on your TimeMachine disk.

To avoid problems, eject the TimeMachine disk before running the upgrade installer.