Inconsistent sizing.  I ordered two of these in medium.  The first one fit my wife just fine, the second was WAY too small.  I sent it back and ordered another thinking it was a fluke.  It too was too small.  I checked the tags both times and they are all the same size.  Other than that, the one that fits seems to be a great product, you just might have to make several returns before getting one that fits.