I am not able to reproduce the issue. Evaluations2.bpmn round-trips fine in the oryx web designer (1.0.0.053 and pretty sure would in 052 as well). Show you entire error in server logs. Most likely is that you are using an older Guvnor version. If you use 1.0.0.053 you need to use Guvnor from master currently (build it yourself).
Thanks.