[XeTeX] Search and replace (removing line break) for chapter title used in header

[Pander]

Hi all,

Is it possible to do a search and replace which removes line breaks from
the chapter's title which I use in (fanncy) header?

Sometimes, the title of a chapter looks better with a manual line break.
This is no problem for the table of contents, it replaces the line break
with a space. Fancy header is not replacing this, resulting in a line
break in the heading.

How can I do this in manually in my definition:
  \fancyhead[LO]{\footnotesize \leftmark}

Or/and is this a bug for fancyheader and how can it be solved there, in
a similar way the table of contents is dealing with this?

Thanks,

Pander