so i forgot to post the solution to this.. turns out the problem was related to the "empty string with //g" issue that plagues PCREv1's demo code. here's the fix:

Code:
; $regexm(<string>, <regex> [, N])[.pos]

; Get the Nth value of match[0] (defaults to N = 1)
; Return its position with .pos

alias regexm {
  noop $regex(full, $2, /^(?|m(.)?|(/)|^)(.*?)(?:\1(?!.*\1)(.*)$)?$/usD)
  noop $regex(pcre, $regmlex(full, 1, 2), /^((?:(?!\((?:(?:MARK|PRUNE|SKIP|THEN|\*(?=:))(?::[^()]*)?|ACCEPT|COMMIT)\))\(\*.*?\))*)(.*)/us)
  if (!$regex( , $+(/, $regmlex(pcre, 1, 1), |, $regmlex(pcre, 1, 2), /))) {
    echo -eagc i * $!regexm: Invalid expression ( $+ $regerrstr $+ )
    return
  }
  var %char, %exp
  while ($chr($r(2048, 55295)) isin $1) /
  %char = $v1
  var %exp = $+(m, $regmlex(full, 1, 1), $regmlex(pcre, 1, 1), (?: $+ $regmlex(pcre, 1, 2) $+ \E)(?(R)|\K), $regmlex(full, 1, 1), $regmlex(full, 1, 3))
  var %str = $regsubex($1, %exp, %char) .
  if (!$pos(%str, %char, $regex($1, $2))) {
    noop $regex(check, $regsubex($1, $2, %char), / %char ( %char ?)/gxu)
    %str = $regsubex(fix, $left(%str, -2), / %char \K/gxu, $regml(check, \n)) .
  }
  noop $regex(final, $left(%str, -2), $+(/\Q, $replacecs($regsubex($1, $2, %char), \E, \E\\E\Q, %char, \E(.*?)\Q $+ %char), \E/u))
  if ($prop == pos) && ($3. isnum 1- $regml(final, 0)) return $calc(1 + $regml(final, $3).pos - $3)
  returnex $regml(final, $3 1)
}

"The only excuse for making a useless script is that one admires it intensely" - Oscar Wilde