I'm not sure of the exact error, but this is the output of diff: (out1.html is perl yourscript.pl > out1.html; out2.html is just copied/pasted from your example above)

buu@its01:~$ diff out1.html out2.html
4c4
< <SCRIPT LANGUAGE="Javascript" type="text/javascript">
---
> <SCRIPT language="Javascript" type="text/javascript">
8c8
<             (o.selected) {
---
>             if (o.selected) {
11a12
>
34,36c35,37
<             <td align="center">
<                 <input class="accessButton" type="button" value="Add
+>>" onClick="moveOptions(this.form.available, this.form.selected;"><b
+r>
<                 <input class="accessButton" type="button" value="<<R
+emove" onClick="moveOptions(this.form.selected, this.form.available;"
+>
---
>             <td>
>                 <input class="accessButton" type="button" value=">>"
+ onClick="moveOptions(this.form.available, this.form.selected);"><br>
>                 <input class="accessButton" type="button" value="<<"
+ onClick="moveOptions(this.form.selected, this.form.available);">
45a47
>
[download]