Redundant calls to UserGroupCallback methods cause performance problems in BPMS 6

Issue

We have implemented a custom UserGroupCallback which interacts with our organization LDAP server.

We have observed that task operations are very slow, due to the custom UserGroupCallback's existsGroup, existsUser and getGroupsForUser methods getting called redundantly:

• Start Process (while user task node is executed)
  • existsUser is called 4 times
    *existsGroup is called 1 time
• Start Task
  • existsUser is called 6 times
  • getGroups is called 7 time
• Complete Task
  • existsUser is called 2 times
  • getGroups is called 3 time

Why does the jbpm engine invoke the callback methods multiple times?