Just wanted to pass this along to anyone else who may be experiencing this.  We moved in several years ago to one of the townhomes, and had the house painted.  Within a short period of time we noticed the paint was cracking along the bottom of the wainscoating in the stairwells.  We thought it was due to the excessive amount of caulk used by the builder, but we have someone working on the house right now who discovered that all of the trim is loose - the builders did not use enough nails when nailing the trim down.  As a result, everytime we walk up and down the stairs, the trim moves a bit, causing the cracking.