Hi, it is a known issue which is also reported here: https://bugs.eclipse.org/bugs/show_bug.cgi?id=357088.
We have pushed a fix to the jBPM web designer recently. Could you please test it out with the latest from master: http://people.redhat.com/tsurdilo/oryx/latest/ and let us know if you still run into issues. Please note that this is NOT AN OFFICIAL RELEASE!
Hope this helps.