> With this I can eval the progn many times. I'm not sure why it's 23
> the first time, then "23 (#o27, #x17, ?\C-w)" all subsequent times:
>
>   23
>   23 (#o27, #x17, ?\C-w) [3 times]

This occurs on trunk, so not a concern of the concurrency branch. I
submitted a bug report.