maven-metadata.xml is outdated for org.mortbaly.jetty:jetty

Updating the artifact metadata should be part of your release procedure. If you look at this:
http://repo2.maven.org/maven2/org/mortbay/jetty/jetty/maven-metadata.xml
you see that that latest 6.x.x is 6.1.16 there. But in fact you have Jetty 6 up to version 6.1.26 in that repo. Thus if someone has:

<dependency>
<groupId>org.mortbay.jetty</groupId>
<artifactId>jetty</artifactId>
<version>[6.1.20,7)</version>
</dependency>

then that will fail, saying there is nothing in that range. Still something like <version>6.1.26</version> would work.