Could it be that a part is missing?
Here's the story. We were about 50 minutes in to a 2 hour Tuesday ride, traveling at about 26-27mph on a slight descent when I hit a bump. Upon striking said bump, my right arm rest was gone!!! K was right behind me, and she said it kinda flew by her head. Luckily, neither one of us ended up with misc. bike parts hitting wheels or anything. It was a little crazy for a second, but I managed to stop without incident.
So, K posted that she thought the holiday weight gain may have been an okay thing. My arm rest might disagree. Turns out I sheared off the bolt that holds it in place. Somebody must have been putting a leeetle extra pressure on the arm rests... ;)