From the NTSB Report:
"The No. 3 engine was recovered from the top of the deicing tank. One blade was impact damaged and near the feather position. The other two blades appeared in a position between low pitch and feather. One propeller blade exhibited a 5-inch tip separation and the separated tip sections were recovered from 100 ft and 700 ft from the main wreckage."
The report did not specifically state that the separated tip sections were from the damaged blade of No.3 engine; however, from the above wording, I think that it can be assumed (dangerous to do) that the No.3 engine blade "... near the feather position." was the one that threw the "separated tip sections" several hundred feet from the impact site. It would take considerable rotational energy to throw propeller blade tip sections several hundred feet from the impact site. It is my understanding that the Hamilton Standard propellers that were fitted to the subject B-17 can have a single blade impacted and damaged to the extent that it will be out of phase with the other blades of the propeller. It is possible that the damaged blade had been in "low pitch" when the impact occurred. Low pitch is usually selected when maximum power is needed. I'm thinking (my thoughts are often proven incorrect) that the No.3 engine may have been providing significant power at impact and was not feathered.
Just more speculation on my part.
Regards,
Grog