Block title lost after theme change

When changing themes, the block title can be lost.

To replicate, do the following:

• Install fresh Drupal 6.0
• Install and enable the Salamander theme (from drupal.org), while keeping Garland installed.
• In salamander, enable the Primary Links block (after putting something in it, eg a contact menu)
• In Salamander, change the title of Primary Links from (empty) to "".
• Observe that the block has no visible title now, this is what we wanted.
• Now, without uninstalling Salamander, switch the site to the Garland theme
• Re-setup the blocks in Garland in order to make Primary Links visible.
• Observe that the title of Primary Links is now "Primary Links".
• Go to block configuration for the Primary Links in Garland, observe that the block's title is configured as "".
• This is not correct: Even though is specified as the title, the title "Primary Links" is visible, which corresponds to an (empty) title in the config.