This photo is of a caulked joint located at a window on a three year old house. As you can see - the caulking has separated from the top materiel - which is the vinyl window frame. The caulking has become hard and brittle and could not stretch as the two materials (vinyl window - and the trim) expand and contract due to temperature differential.
The caulk is more then likely a carbon based acrylic sealant - and also the incorrect material to use in this application. The subcontractor should have used a higher quality silicone adhesive sealant. Silicone has several advantages over acrylic when it comes to choosing a caulk. The best is longevity. It does not have to replaced every few years like this acrylic caulk. As an example of silicone's longevity - a building in Atlanta built in 1969 still had working silicone sealant joints when the sealant was replaced as part of a remodeling upgrade. Silicone also does not get brittle, adheres better, and is not affected by temperatures extremes like the acrylic caulking. Silicone may cost more but it is worth the extra money for the better sealing and lower maintenance.