The problem appears to have been caused by the content of META-INF/drools.rulebase.conf which is modified by the import process.
The content of this file should contain a line like this:
drools.workDefinitions = Twitter.wid Email.wid
In the version that didn't work, the *.wid files were on separate lines and only the first of these was showing on the sidebar.
Hope this helps someone.
Andy McC