Yaw Control Factors
A friend of mine is familiar with the background on this aircraft and who knew the pilot has suggested that the yaw stability of the aircraft was not wonderful and speculated that an event like loss of an engine or other yaw inducing event could potentially cause a loss of control.
This aircraft incorporated pioneering design features and there may have been handling characteristics that would not have been acceptable in a regular production aircraft.
A comment from the preliminary NTSB report seems to suggest that the pilot was preparing to bail out: " several witnesses reported that after the maneuver, the airplane "wobbled [from] side to side" before the airplane's canopy separated."