Imagecache theme function does not use default image setting

I've just upgraded imagecache (5.x-2.3) to use the imagefield (5.x-2.4) default image.

While the formatters have been sucessfully updated in imagefield.module so that Views display the selected preset's default image. The theme_imagecache function doesn't seem to do this. It returns broken image URL's if there is no image in the imagefield.

How can I use the theme_imagecache function in my .tpl files to automatically generate/supply the default image for a namespace preset? I realise I could code logic into my .tpl, but I think image cache would be better to respect the imagefield's default image and automatically generate the default preset images.

NB: Is this an imagefield.module issue?