it sounds like they didn't have a way to verify that the lower stage had finished its burn, before attempting separation. this is a good lesson in vehicle design :P
From the page: "Gravity gradient stabilization.
In orbit, a spacecraft with one axis much longer than the other two will spontaneously orient so that its long axis points at the planet's center of mass. This system has the virtue of needing no active control system or expenditure of fuel. The effect is caused by a tidal force."
From the page: "To the surprise of mission experts, satellite Explorer 1 changed rotation axis after launch. The elongated body of the spacecraft had been supposed to spin about its long (least-inertia) axis but refused to do so, and instead started precessing due to energy dissipation from flexible structural elements."
Paul MacCready gives a charming talk mainly about his Gossamer human powered aircraft... and how he started that project to win the prizes that got him out of debt :)
"...provides full color visual examples of acceptance / rejection criteria which may be used for the design, manufacture and inspection of electrical / electronic equipment for high-reliability and space flight applications..."