Look in your .../deploy/jbossweb.sar/META-INF/jboss-service.xml
see this ?
Jetty is configured to start with a pool of 10 request threads, and allocate up to 100 to service requests. When you hit 100 a request has to wait for another to finish before it can reuse it's thread.
It looks like your tool has backed up more than 100 requests. Give Jetty more threads and see what happens.