I am going to take a stab at it and suggest that because we both spent the majority of time on one thing (classical for myself, improvised for Chris) that is why those things came back the fastest. I didn't have to think about improvised music all that much so when I did, it was a challenge. Chris had the freedom from orchestral parts, so when it did come around it was challenging.
Don's story about Red Mitchell is comically close to one that Joel tells about his switch. He was playing a quintet with a pretty well known string quartet (Tokyo maybe?) and went to grab a not that was no longer there with the enthusiasm and assertion that his playing is known for. I think the electric guys call what resulted a "hammer on" and it was decidedly quite rock and roll for the music they were playing.
There definitely are "4ths moments" that happen to all of us who have made the switch, sometimes years later. Unless you get a look from a conductor or a bandmate, I've learned not to acknowledge them. It's frightening how often I would apologize for one in a chamber music rehearsal right after the switch, and the rest of the ensemble didn't notice what happened at all. A bass player friend told me this years ago and it seems to have treated him well through his professional career: everyone makes mistakes. You just need to correct them faster than the other guy.
