In a survey of the comments and returned sets, service manager Scott Hecker of Boxer Shelving concluded that the connector of the two upright posts is still coming out wrong from the plant. In 2015 so far, 941 units were sold but only one returned.
The parts are just supposed to tap in with a hammer or mallet. The connector is too tight. The handymen apparently all discovered that you can expand the crack enough with a flat headed screw driver hammer and a wood block for support.
The joint then can be tapped into place and the second support rod connected for the top half of the shelf. "I've contacted the plant three times," says Scott, "but nothing changes."