Designer currently supports strictly what the jBPM runtime currently supports. As we add things to the runtime, we also add it to Designer. We could support the entire BPMN2 spec however it's a trade-off because we focus on being able to create executable business processes in the jBPM 5 runtime. Looking at your bpmn2, Designer would not understand the collaborations and multiple process elements (pools) as the runtime does not support that yet.
Hope this helps.