Jumping Chain

Andrew, I had a strange occurrence today. I got out on the bike and did 21 miles with an average speed of 13.6 with LOTS of stop lights and 20 minutes or so of that into 10 mph wind and probably averaging around 14.5 during that time.

When I started the chain was jumping as if it had a bent spot on it. I kept stopping and adjusting it because I though I might simply have the derailleur misaligned. (I exchanged wheelsets between bikes)

But it was jumping just like it had a bent link. Now it was a good chain with little mileage on it. The distance between the jumps was about a chain length. I looked at the master link since this was a "gold" chain that came with one of those crooked master links which are supposed to be reusable. But I had replaced it with a normal master link.

As I covered the first 10 miles the jumping got progressively less and less until it disappeared.

Have you got any suggestions of what might have caused that?