Hi Jaikiran,
I found an answer to my problem (thanks to your suggestion). I skipped some files in the structure I posted before as I assumed they were insignificant. I was wrong again. It turns out I put a jboss-scanning.xml to work around the JBAS-8361 issue (richfaces with guava). I must have been blind not to see it before.
Anyhow, thanks a lot for your help.
Just for reference, this was my jboss-scanning.xml file:
<scanning xmlns="urn:jboss:scanning:1.0">
<!--
For JBoss AS 6 integration there is a conflict with guava, and
google-collections. JBAS-8361
-->
<path name="WEB-INF/classes"></path>
<path name="WEB-INF/lib/guava-r05.jar">
<exclude name="com.google.common.collect" />
</path>
</scanning>
{code}
This obviously defines the 'includes' and overrides the default scanning paths. I added the <path name="WEB-INF/lib"></path> tag at the end in order to get JBoss to scan the whole lib directory.