This is just to bring you back to the top.
The reason is, the "existing files" are associated with the "a" drive, either from being written too, or copied from the drive originally, so each time you open one of them it will first look at the "a" drive then move on.
The solution is to re-move the association, and I've forgot how to do it! But not to worry, someone will help us both on this tricky little problem. ;o)