wab expanded directory can not be cleaned while having fragments.
Reproduced Steps are as following:
1 asadmin deploy --type=osgi sample.uas.api.jar
2 asadmin deploy --type=osgi sample.uas.simplewabfragment.jar
3 asadmin deploy --type=osgi sample.uas.simplewab.war
4 asadmin undeploy sample.uas.simplewab
5 entering into OS temp directory, and you will find the following file(eg. in my env) is not deleted
osgiapp569463777010148476\WEB-INF\lib\Bundle290.jar, and Bundle290 is the fragment bundle id.
So, the fragment bundle must be in use.