Carpentry and Woodworking - new construction wood trim separating

Our newly constructed house is not quite 2 years old. We paid the builder a pretty good sum in addition to the agreed upon purchase price to create a square columned entryway to our living room and to add crown moldings in certain rooms. Now, 20 months after completion, the wood at the tops and bottoms of the columns is separating from the top and bottom pieces of the entryway structure, with gaps of 1/8" to 1/4" inch visible and quite noticeable. Smaller pieces of the wood which makes up the columns are warping and curve visibly outwards. In addition, all of the molding is separating from the walls, with visible gaps of about 1/8" to 3/16" between the molding and the walls. The wood is separating by about about 1/8" to 3/16" where the angles meet on the fireplace mantle. And finally, the 45 degree angles where the wood meets in the corners of all the doorways and window trimwork are separating, by less than 1/16", but in a noticeable way. The gaps show up as what look like 45 degree angled, straight black lines in the white trim.
The builder is a reasonable and accommodating guy, but is incredibly busy and in demand, and has told us that he can fix everything by simply caulking and repainting. We’re wondering what caused the problem and what the proper fix would be. We suspect that, as the builder was behind schedule for our closing and move-in, that to meet the closing deadline and get the CO he put up the molding, mantle, and entryway wood without letting it dry out, and/or put it up over plaster that was not fully dry. If a caulk and repaint is all it takes, great, but if this would only cover the problems up for another year or so then we would like to know what should be done to get us what we wanted, and paid extra for, when we first moved in.