The IURC reversed itself after it reopened the matter in the wake of an ethics case that followed Duke Energy's hire of the IURC's former chief counsel, Scott Storms.
Storms, who had been both the commission's top attorney and its administrative law judge, was fired by Duke Energy in November 2010 after just two months on the job after it came to light that he discussed a position with Duke Energy while presiding over hearings.
Gov. Mitch Daniels also ousted the utility commission's then-chairman, David Lott Hardy, saying he knew about Storms' ethical conflict but did nothing about it.
An internal audit by the commission found no evidence that Storms exerted "undue influence" on the panel's decisions. The storm damage case is the only one the panel reopened following the ethics case.
Although Duke Energy had contended that the two opposite decisions were based on the same evidence, Friday's ruling said that wasn't the case.
Among the court's findings is that the commission's second order was based only on the ice storm case, while the panel in its initial decision considered the impact of both a September 2008 windstorm and the ice storm that four months later left tens of thousands of southern Indiana residents without power for days.