XML parser: Missing a 'outputSet' element in 'ioSpecification' element for Multiple instances subprocess

Description of problem:
jBPM Designer does not generate a 'outputSet' element in the 'ioSpecification' element in Multiple instances subprocess.

But the 'ioSpecification' element requires both elements (outputSet as well as inputSet). The cardinality of both elements are from 1 to *.

Saving of such process causes ERROR in server.log:

ERROR [org.drools.core.xml.ExtensibleXmlParser] (EJB default - 1) (null: 21, 31): cvc-complex-type.2.4.b: The content of element 'bpmn2:ioSpecification' is not complete. One of '

{"http://www.omg.org/spec/BPMN/20100524/MODEL":inputSet, "http://www.omg.org/spec/BPMN/20100524/MODEL":outputSet}

' is expected.

The outputSet element is not present even if I set the 'MI collection Output' property. The value of this property is lost after reopenning of process.

Version-Release number of selected component (if applicable):
6.1.0 ER3 BPMS

Steps to Reproduce:
1. Create new process (Start -> MI Subprocess -> End
2. Define Process Variables "test:String,test2:String"
3. Activate MI subprocess
4. Choose "test" in the "MI collection input" property.
5. Choose "test2" in the "MI collection output" property.
6. Show BPMN2 source code
7. Reopen process

Actual results:
Step 6:
<bpmn2:ioSpecification id="__qIZsZTnEeSgV5GYSrrD3w">
<bpmn2:dataInput id="_67ADB665-29CE-4F4E-8F1B-B46253B2E800_input" name="test"/>
<bpmn2:inputSet id="__qIZspTnEeSgV5GYSrrD3w">
<bpmn2:dataInputRefs>_67ADB665-29CE-4F4E-8F1B-B46253B2E800_input</bpmn2:dataInputRefs>
</bpmn2:inputSet>
</bpmn2:ioSpecification>

Step 7: The value of the "MI collection output" property is empty.

Expected results:
Step 6:

When MI collection output is not set:
<bpmn2:ioSpecification id="...">
<bpmn2:dataInput id="..." name="test"/>
<bpmn2:inputSet id="...">
<bpmn2:dataInputRefs>...</bpmn2:dataInputRefs>
</bpmn2:inputSet>
<bpmn2:outputSet id="..."/>
</bpmn2:ioSpecification>

When MI collection output is set:
<bpmn2:ioSpecification id="...">
<bpmn2:dataInput id="..." name="test"/>
<bpmn2:dataOutput id="..." name="test2"/>
<bpmn2:inputSet id="...">
<bpmn2:dataInputRefs>...</bpmn2:dataInputRefs>
</bpmn2:inputSet>
<bpmn2:outputSet id="...">
<bpmn2:dataOutputRefs>...</bpmn2:dataOutputRefs>
</bpmn2:outputSet>
</bpmn2:ioSpecification>

Step 7: The "MI collection output" property contains a saved value.

Additional info: