I copied a CD to my hard disk by dragging the CD icon to a hard disk icon when using Mac OS 8.1. The copy went normally except that the number of items left to copy eventually went into negative numbers. For example, the progress went 1 --> 0 --> -1.
Solution
This is addressed in a newer version of Mac OS.
Note: This is a cosmetic issue with Mac OS 8.1 and appears to occur only when copying one volume to another. If the source is a folder or a group of files and/or folders, the negative numbers do not appear. There is no data lost.