Better yet, don't use XML::Simple.

And your XML::<Suggested Module/> is ___ ?
It's a tough forest to thin.

 <BILLING name="ADDACCOUNTDETAILS">
      <ADDACCOUNTDETAILS name="RTN" />
      <ADDACCOUNTDETAILS name="ACCOUNT" />
 </BILLING>
[download]

No, it doesn't. First, it worked fine with any change whatsoever. Second, it works with without NoAttr too. It even produces the same tree in both cases.

use strict;
use warnings;

use Data::Dumper;
use XML::Simple;

# The fastest existing backend for XML::Simple.
local $XML::Simple::PREFERRED_PARSER = 'XML::Parser';

my $xs = XML::Simple->new(
   NoAttr         => $ARGV[0],
   KeepRoot       => 1,
   NormaliseSpace => 1,
);

my $tree = $xs->parse_string( <<'__EOI__' );
<BILLING>
 <ACCOUNT></ACCOUNT>
 <RTN></RTN>
</BILLING>
__EOI__

print( Dumper( $tree ) );

print( $xs->XMLout( $tree ) );
[download]

$ perl a.pl 1
$VAR1 = {
          'BILLING' => {
                       'RTN' => {},
                       'ACCOUNT' => {}
                     }
        };
<BILLING>
  <ACCOUNT></ACCOUNT>
  <RTN></RTN>
</BILLING>
[download]

$ perl a.pl 0
$VAR1 = {
          'BILLING' => {
                       'RTN' => {},
                       'ACCOUNT' => {}
                     }
        };
<BILLING>
  <ACCOUNT></ACCOUNT>
  <RTN></RTN>
</BILLING>
[download]

Update: I originally said it produced a different structures.

Yes on that string it works... Might I add a more specific case where it occurs. Ran the following xml with your code...

XML

<BILLING> 
    <ADDTELE1></ADDTELE1>
    <ADDTELE2></ADDTELE2>
    <ADDEMAIL></ADDEMAIL>
    <ADDACCOUNTDETAILS>
     <ADDACCOUNT>
      <ACCOUNT></ACCOUNT> 
      <RTN></RTN>
     </ADDACCOUNT>
    </ADDACCOUNTDETAILS>
</BILLING>
[download]

NoAttr=>0

$VAR1 = {
          'BILLING' => {
                       'ADDEMAIL' => {},
                       'ADDTELE2' => {},
                       'ADDACCOUNTDETAILS' => {
                                              'ADDACCOUNT' => {
                                                              'RTN' =>
+ {},
                                                              'ACCOUNT
+' => {}
                                                            }
                                            },
                       'ADDTELE1' => {}
                     }
        };
<BILLING>
  <ADDACCOUNTDETAILS name="ADDACCOUNT">
    <ACCOUNT></ACCOUNT>
    <RTN></RTN>
  </ADDACCOUNTDETAILS>
  <ADDEMAIL></ADDEMAIL>
  <ADDTELE1></ADDTELE1>
  <ADDTELE2></ADDTELE2>
</BILLING>
[download]

NoAttr=>1

$VAR1 = {
          'BILLING' => {
                       'ADDEMAIL' => {},
                       'ADDTELE2' => {},
                       'ADDACCOUNTDETAILS' => {
                                              'ADDACCOUNT' => {
                                                              'RTN' =>
+ {},
                                                              'ACCOUNT
+' => {}
                                                            }
                                            },
                       'ADDTELE1' => {}
                     }
        };
<BILLING>
  <ADDACCOUNTDETAILS>
    <name>ADDACCOUNT</name>
    <ACCOUNT></ACCOUNT>
    <RTN></RTN>
  </ADDACCOUNTDETAILS>
  <ADDEMAIL></ADDEMAIL>
  <ADDTELE1></ADDTELE1>
  <ADDTELE2></ADDTELE2>
</BILLING>
[download]

You are right, ForceArray=>1 works. It keeps everything in format, except the order which shouldn't matter in my case.
The only issue I am having now is parsing through the tree. I am trying to write a recursive function to walk through this hash of array/hashes, which is proving to be difficult.