This isn't very elegant, but you could scatter print statements through the suspect areas to see what is being executed and in what order and what your variable values are.

$tesing = 1;
   .
   .
print "At second 'if' in do-loop, \$target_name is $target_name" if ($
+testing);
   .
   .
[download]

(untested)
Or something similar.

Theo