After discussion during a weekly call we concluded that while in theory this is a problem developers can avoid this type of problem. For example a client should not simple assume the single returned NodeId in the TranslateBrowsePathsToNodeId response is the optional Node without further investigation of the Node (is it the expected VariableType, etc).

It was agreed the second issue "Clarification is needed to state that a subtype can not reuse the BrowseName of an Optional Node of any of its parents" should be incorporated into Part 3.

Agreed to move this issue to Part 4 and clarify how Clients need to protect themselves by checking the type when they call TranslateBrowsePathToNodeIds.

5.8.4 TranslateBrowsePathsToNodeIds
5.8.4.1 Description

Added following clarification:
If a type definition has optional elements, the Server may return one target that is not based on the type definition. Clients should be prepared for this case and always check additional expected behaviour like the DataType of a Variable.

Updated in OPC 10000-4 - UA Specification Part 4 - Services 1.05.0 Draft11.docx

We need to define in Part 3 that it is not allowed to add component to an instance, it can not the same browse name as an optional component defined by the type if the optional component is not there.

Added the following statement to 6.4.4.4.2 Optional:
"Instances shall not use the BrowseName of a Node which is defined with the Optional ModellingRule for any other Node. In other words, even though an instance may not provide the Optional Node it shall not redefine its TypeDefinition."

After a long discussion we concluded that we need to fix the root cause of this issue rather than continue to define specific cases.

A general statement that defines "No instance can declare a target of a hierarchical reference that has the same BrowsePath as an InstanceDeclaration of its TypeDefinintion which has an optional or mandatory modelling rule." This should be added to 6.4.2.

Need to clone to Part 4 after we agree on the updated text.

Added the general statement about instance defined Components in 6.4.2 Creating an Instance.

Needs 1.04 Errata to close.

Agreed to 1.04 Errata in Telecon.