Here's the sub that prints the debug message and appends the content:

sub verbose_add_content {
  printf "depth: %d adding: ((%s))\n", $depth, $_[1];
  $_[0] .= $_[1]
}
[download]

As we can see, it prints $_[1] and appends $_[1]. Of course, the value of $_[1] should be exactly the same each time (barring a weird use of tied scalars).

So, my best guess is that something else is going on. Is it possible that the script you're editing and the script you're running are two different files? I've made that mistake a few times.

If the bug doesn't reveal itself soon, you may want to package up all the files involved, put them on the web, and post a link, so that other monks can download it and run the same test you're using.