Make sure they are de-laminating and it's not just the sheets of leather spreading.
Remember the sole and particularly the heal block are made from a number of sheets of leather - as you walk the leather will compress and expand / stretch ever so slightly which can make it look like the sole / heel are coming away if one sheet of leather spreads / moves more then the next. This is most noticeable on the lower most sheet on the sole, and the sheet above the rubber heel block, it can also be made worse if you let the leather get saturated.
When you say the first pair the sole was coming away - what was happening to the stitching that was holding the sole to the welt - was it broken?