If a project has a dependency to JSF 2.1, like :

<dependency>
    <groupId>javax.faces</groupId>
    <artifactId>jsf-api</artifactId>
    <version>2.1</version>
    <scope>provided</scope>
</dependency>

no JSF Facet is installed. The JSF Facet 2.1 is only available in Juno, so it cannot be installed, but JBT should at least fall back on the highest facet version available (2.0)