I think your conclusion is correct in general, but if you know the structure of the RE then there are workarounds to the way the capture groups work. Consider:

#!C:/strawberry/perl/bin/perl.exe
#
use strict;
use warnings;
 
my $string = "aacbbbcac";
 
my $re1 = qr/((a+)?(b+)?(c))*/;
#my $re1 = qr/((a*)(b*)(c))*/;
#my $re1 = qr/((a+)?(b*)(c))*/;
if ($string =~ $re1) {
  my $start = 0;
  my @something;
  foreach (0..$#-) {
    if(defined($-[$_])) {
        $start = $-[$_] if($-[$_] > $start);
        if($-[$_] >= $start) {
            printf "Group %d: <%s>\n", $_, substr($string, $-[$_], $+[
+$_] - $-[$_]);
            $something[$_] = substr($string, $-[$_], $+[$_] - $-[$_]);
        } else {
            printf "Group %d: <%s> - but ignore it because it is from 
+a previous iteration of the outer capture group\n", $_, substr($strin
+g, $-[$_], $+[$_] - $-[$_]);
            $something[$_] = '';
        }
    } else {
            printf "Group %d: hasn't matched yet\n", $_;
            $something[$_] = '';
    }
  }

  print "$1 = " . join('', @something[2..4]) . "\n";
}
[download]

Which produces

Group 0: <aacbbbcac>
Group 1: <ac>
Group 2: <a>
Group 3: <bbb> - but ignore it because it is from a previous iteration
+ of the outer capture group
Group 4: <c>
ac = ac
[download]

If you are trying to write something that handles arbitrary REs, this approach is unlikely to work.