Indexterm in title

Hi,


When i place a indexterm-tag in a title tag:


<section>
<title>
<indexterm>
<primary>some_indexterm</primary>
</indexterm>
</title>
...

i get this error message:

"no entries for index key: some_indexterm"

And the index gets a "?" instead of page numbers behind some_indexterm.

Im using docbook-xsl 1.62 and XEP.

Is this a known problem?


Thx,

Sebastian