You don't have that right!  The progress bar is a totally different task from the one that it's reporting on.  The base task can totally crash, and the progress bar will go on reporting progress, for hours!  For example, when copying a file, the little papers continue to fly and the bar advance, even when the source disk becomes unreadable or sector read error, or when copying stops because computer is demanding response from you (such as whether you want next file overwritten).