Forgot to describe the configuration :
jboss 4.0.4.GA with jbossws 1.0.3.GA
I check the source again and I still don't understand what's going on.
Should I post a bug report in jira ?
I found where the problem is comming from.
My 20 threads were using the same Call instance. When I create 1 call instance for each thread there is no problem.
Is javax.xml.rpc.Call implementation in Jbossws 1.0.3.GA threasafe ?
Service is threadsafe, Call has invocational state.