>
> !Changing the last line to (substring pcomplete-stub 1 -2) fixes it in my
> example. I don't know if one is supposed to do [[*prefix<c-a-p>]] or
> [[*prefix<c-a-p> as is implied by the code, but better to support both,
> specially considering electric pairs, don't you think?
>

Indeed, the right limit should be the position of the point.