Last night I remembered something that might be relevant. While I was waiting for my Surly single-speed cog to arrive, I set up my Highlander as a single-speed using a 7-speed cassette and using the long dropouts to adjust chain tension to keep the chain on the correct cog. I rode easy and this worked for the most part but there were a handful of times when the chain jumped to next larger cog and immediately locked the cranks. Each time I was simply sitting and pedaling, rather than hammering it, but it still pulled the hub out of alignment in the dropouts. Might this have possibly bent something? It's the only thing I can think of that might have caused the widening issue.