Scrolled list behaviour

I and one of my users have found a change in the behaviour of scrolled
lists running Perl Tk on Windows XP.
 
I create the lists using the $parent->Scrolled('Listbox',
and create the scroll bars with -scrollbars =>'osoe'
 
I now find that sometimes the scrollbars do not work even when the list
is say longer that the list box is high.  I thought that this may be due
to a problem with the Perl version I have recently started to use which
is 5.8.7.  However, I have tried this with 5.8.4 and I find the 'bad'
behaviour there as well although I am reasonably sure it was working OK
with this version.
 
I then tried creating the scroll bars with -scrollbars =>'se' and the
behaviour returned to what I wanted.
 
I wondered if anyone else had found a similar thing and if there is
something a little odd with the osoe option.
 
Best regards
 
Henry Merryweather