$r->dir_config->(un)set issue...

Hi All, 

I have a situation where it is convinent for me to define a global
"PerlSetVar" in my httpd.conf and then unset it for particular virtual
hosts. 

I used to use the following configuration successfully:

----------------------------------------------------
httpd.conf
----------

<Perl>
  use Apache::Server;
  Apache->server->dir_config->unset("MyVar");
</Perl>

-----------------------------------------------------

That stopped working for me ever since we compiled 
Apache/1.3.26 (Linix - Debian) with mod_perl/1.27


Has anyone else had the same issue? 

On a similar note: 

The following pices of code do not work:

-----------------------------------------------------
code sample 1
--------------

1.  sub handler {
2.    my $r = instance Apache::Request(shift);
3. 
4.    $r->dir_config(MyVar => undef);
5.   
6.    $r->dir_config->unset("MyVar");
7.
8.    $r->dir_config->set(MyVar => undef);
9.
10. }
  

None of lines 4, 6 or 8 actually unset the variable. 

A collegue tells me that if a "true" value (for the key MyVar) is not
passed to set then it ends up returning the value of MyVar - but then
how i want to set the value of MyVar to be false. I would have though
that unset/set would have specifically done what i told them to
unset/set rather than do fancy things with truth values... 

Ideas anyone? 

simran.