Similar event in Gander years ago Smudge, where we had freezing rain after landing, after deice and walk round by eng and driver airframe satisfied all was good to go. On starting 3 Albert begins to shake itself rather violently. Captain asks ALM what's going on , reply along the lines of " if I was allowed to call stop start I'd be doing it now! " shut down and further walk round revealed a layer of clear ice on every prop blade.