feisty upgrade: update-manager doesn't find enough disk space

[H.S.]

While doing the upgrade from fully updated Edgy to Feisty, the 
update-manager reports that around 70 MB disk should be freed in 
/var/cache/apt/archives. However, I have more than enough disk space 
there. I have also followed the tip about putting the following line in 
/etc/apt/apt.conf (from the release notes for Feisty), even though my 
archives directory was not a symlink:
----------------------------------------------------------------------
     * Update Manager may incorrectly calculate the free space 
requirements when symlinks are used for some directories such as 
/var/cache/apt/archives. Bug #106804. As a workaround, modify 
/etc/apt/apt.conf and add the following line giving the correct path for 
that directory rather than using a symlink.

         Dir::Cache::archives "/path/to/your/apt/archives";
----------------------------------------------------------------------

but update-manager reports the same problem. What should I try?

->HS