Hi Tobias, wow presenting your errors via videos is really cool! Thank you very much.
Issue #1: This issue goes back to the eclipse.bpmn2 ecore model which does not make sure the id property of the definitions node is of type xsd:NCName. I am working on fixing this in their ecore model and should have done soon.
Issue #2: Yes this is also a known Issue which I'm working on in Guvnor. When saving the process Guvnor gets the process JSON from the canvas (via JavaScript) and sends it over to Designer to convert it to BPMN2 format. If Designer is not able to to parse the JSON (because of simple issues or larger) it sends back a blank string to Guvnor, thus your process BPMN2 is gone. Best thing I can advise you until this is fixed to make sure you view the source becore saving your process changes. View source actually does the same steps (except saving bpmn2 in Guvnor) so you will see any possible errors without loosing them in Guvnor.
We will also add a validation button to the toolbar which will allow you to view any errors/warnings before saving your process. Should have that done in about 3-5 weeks.
Issue #3: Again this goes to the eclipse.bpmn2 ecore model. If you look at Semantic.xsd it defines a sequence for the process element:
<xsd:element name="process" type="tProcess" substitutionGroup="rootElement"/>
<xsd:complexType name="tProcess">
<xsd:complexContent>
<xsd:extension base="tCallableElement">
<xsd:sequence>
<xsd:element ref="auditing" minOccurs="0" maxOccurs="1"/>
<xsd:element ref="monitoring" minOccurs="0" maxOccurs="1"/>
<xsd:element ref="property" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element ref="laneSet" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element ref="flowElement" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element ref="artifact" minOccurs="0" maxOccurs="unbounded"/>
<xsd:element name="supports" type="xsd:QName" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="processType" type="tProcessType" default="none"/>
<xsd:attribute name="isClosed" type="xsd:boolean" default="false"/>
<xsd:attribute name="definitionalCollaborationRef" type="xsd:QName" use="optional"/>
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>
however when generating bpmn2 eclipse.bpmn2 does not seem to follow this sequence correctly. I'll look into this and will provide more info soon.
Issue #4: What Designer version are you testing with? Please show the bpmn2 shown in the xml editor of your video.
Thanks again for reporting all this :)