Preset does not render because language prefix is not included in the imagecache URL

I have a weird behaviour in a multisite installation, working on a small 2-language site (public files and php 5.2.9).

I created a language enabled nodetype with an imagefiled. The imagefiled is set to display as an imagecache preset on body view.

If the imagecache image does not exist yet, it does not show up when going to the node page. If I enter the imagecache URL, my homepage comes up. The URL is the usual imagecache one http://domain.com/sites/domain.com/files/imagecache/preset/pathtofile.jpg (same happens with sample image)

Doing some trial and error, I found out that the imagecache URL will process OK if I add a language prefix to the URL: http://domain.com/es/sites/domain.com/files/imagecache/preset/pathtofile.jpg

From there on, the imagecache is available with any URL (with and without prefix) and it obviously shows on node view.

I have checked the troubleshooting page, but those solutions did not work for me, and I don't think it is a rewrite issue because:
- if I use the same imagecache url pointing to a non-existing file http://domain.com/es/sites/domain.com/files/imagecache/preset/nonexisting.jpg it renders a blank page
- if I use a normal filepath url: http://domain.com/es/sites/domain.com/files/pathtofile.jpg the file is there
- if I use a normal filpath url pointing to a non existing file: http://domain.com/es/sites/domain.com/files/imagecache/preset/nonexisting.jpg it gives a 'page not found' error

Is this the normal behaviour or is it a bug? Is there a workaround for adding a language prefix to imagecache URLs?

I hope you can help. Thanks in advance.