Thanks, Mike. In the first keyframe, I noticed that most of the bones in the upper body were no longer connected to the body parts, so I clicked each bone, then held down the "b" key and clicked body parts to reconnect. I only did this in the first keyframe. I didn't think of it at the time, but I would bet that the problem would have gone away if I went to all the keyframes and reconnected the bones before I moved anything.
I finally got around the problem by deleting the entire upper body on all but the first keyframe, editing the first keyframe, and pasting the edited upper body that I leaned forward, into all the other keyframes. That worked.
Do you think there would be an issue between the previous version and your latest version that could cause the bones to disconnect from body parts? I still love Spriter. Great software, thanks for making it.