JT seems to have covered much of what I may have put in. All I can add is that we often used to block rows out for trim to avoid what happened to Matthewc. Confused the hell out of the pax, but was always a last resort. Never rely on pax seating for trim, always an unknown factor as they tend to move about, even if told by the seagulls not to.
Another thought was perhaps the acft had a fuel problem on one side & couldn't centre it? Highly unlikely I know & I've never loaded pax laterally for anything like that, but something perhaps to consider.