Danke sehr! Four trips to summer German Camp were not wasted!
The immediate problem is those "bone position" channels which may be useful for something but in this case are really making a mess. Pasting rotate and translate keys shouldn't be creating those.
If I delete them all, the animation will return to normal
You're on to something here! If I turn off the Translate filter before I do the paste, i don't seem to get Bone Position channels.
However, I need to have the Translate filter on because I need to paste translate keys.
The work around for all of this is to have "Key Bone" on when you do the copy of several bones (as i did in the video) THEN turn on "Key Model" before you do the Paste.
This will paste the keys correctly without creating the problem Bone Position keys.
It's possible this is the correct workflow anyway, but I haven't checked to see how previous version handled this.