When changing the type from Java Class to Expression in the property editor the BPM2.0.xml does not change until the complete diagram is closed and reopened again.
1. Create ServiceTask with class as delegation and choose a class
2. Save the diagram
(close and reopen the diagram editor (not sure if this needs to be done))
3. Change the ServiceTask to expression and fill in an expression
4. Save the diagram
5. OPen the bpm2.0 view --> it still references the Class specified in step 1
6. Close the diagram editor and reopen the diagram
7. OPen the bpm2.0 view --> it shows the expression.