Hi Igor,
I believe the problem is in:
(defun pcomplete/org-mode/searchhead ()
...
;; When completing a bracketed link, i.e., "[[*", argument
;; starts at the star, so remove this character.
(substring pcomplete-stub 1)))) <-- trailing ]] not removed!
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?
Best regards,
Carlos