Audio sliding out of sync within clips???

Hello Friends and Countrymen,

I'm not sure the best way to ask this question so I'm going to try and explain....

I'm editing an audiobook, and I let my narrator record himself at my work station and he knows how to punch in record and punch out and sometimes will want to try a certain line several times. So the first thing I did was take all the little clips and "arrange" them in correct order, somtimes manually creating fades, sometimes using the auto cross fades, but anyways. I save the file and now several days later I'm back into it to do more advanced noise removal, compression, etc. But the strangest thing is happening. a great many of my clips are still arranged correctly, but the audio within the individual clips has been slid forward or backwards so the timing is off. Often, but taking the slip tool I'm able to just slide the audio and visually see where it should fit  before I even test listen to it, and it does not take long to fix or do some re arranging. But my question is: DOES ANYONE HAVE ANY IDEA WHAT I DID TO CAUSE THIS MAJOR MALFUNCTION?

The slip tool is just simply not somthing I use often so it's not likely that was it, but can someone think of any error I could have been making (maybe when I was arranging other tracks within the multitrack) because I'm just trying to learn and improve.