Anchor Support for attachments

On a page I have a html document attached and I link to that document:

[[Some HTML Document>>attach:MySpace.MyPage@myattachedfile.html]]

This is working fine.

But the attached html document is very large and contains a lot of
anchors for easier navigation inside the document.
So I'd like to improve the xwiki link to point directly to one of these
anchors in the html attachment.
I modified the link:

[[Some HTML Document>>attach:MySpace.MyPage@myattachedfile.html#someAnchor]]

But unfortunately this is not working. The hash is always escaped.