I thought I replicated the OP's code, but did not have a problem with the post-increment of the array element. So, I am confused that my code seems to work, whereas the OP's does not.

Note how my output does increment the elements. Did I present code that replicates the OP's scenario, or am I off target here?

The difference is that you are actually printing the thing you are incrementing rather than incrementing one item and printing another completely distinct item. What the OP did is more like the final print statement here:

perl -E '
  my ( $x, $y, $z ) = ( 1, 2, 3 );
  my @a = ( $x, $y, $z );
  say join " ", map { $_++, $_ } @a;
  say "@a";
  say "$x $y $z";
'
1 2 2 3 3 4
2 3 4
1 2 3
[download]

Well, let me just

 perl -E '
         say "Thanks!"
       '
[download]