The tumbling seen as the two stages separated was actually not unexpected and Ess said he misspoke at the press briefing on the day of the test flight as the separation being "interesting" (and his team immediately let him hear about it!). "We've actually done thousands of animations showing this type of behavior on the upper stage, and the models predicted this is what we would see. It was the manager who didn't say it right," Ess joked.

 

The upper stage on the test flight was a "dummy" and didn't have a motor, so it behaved exactly as a heavy, unstable projectile would. "Once you separate, there's nothing to control it," Ess said. "In reality, the Ares I will have the J-2X engine on it, and everything will be fine."

 

http://www.universetoday.com/2009/10/30/ares-i-x-manager-addresses-booster-damage-stage-tumbling-and-thrust-oscillation/