ScottCD
Wings level and no flaps retracted.
Do you perhaps mean that no flaps were
extended? ie flaps were up?
What exactly made you think that the left engine was "unfeathered slightly"? Was the noise from the engine uneven or hunting, or did it sound as though it was "missing", like a car running on three cylinders for example?
The ATSB will almost certainly ask you those questions, but the answers could help us here on the forum build a more accurate picture of what was happening.