BPM Suite 6.0.x running on Tomcat7 returns http 409 error on complete task when using rest call

Issue

http 409 error is experienced when trying to complete a human task using rest call (i.e. business-central/rest/task/99/complete) in BPM Suite 6.0.x running on Tomcat7. The same test case works if BPM Suite is running on EAP 6:

2014-07-23 14:00:07,245 [http-bio-8080-exec-2] WARN  Exception thrown when processing request [/task/99/complete]; responding with status 409
org.kie.services.remote.rest.exception.RestOperationException: User '[UserImpl:'user1']' was unable to execution operation 'Complete' on task id 99 due to a no 'current status' match
    at org.kie.services.remote.rest.exception.RestOperationException.conflict(RestOperationException.java:114) ~[kie-services-remote-6.0.2-redhat-6.jar:6.0.2-redhat-6]
...
Caused by: org.jbpm.services.task.exception.PermissionDeniedException: User '[UserImpl:'user1']' was unable to execution operation 'Complete' on task id 99 due to a no 'current status' match