On what server are you trying to run this? I'll bet you can only get the flow scope to work on Glassfish 4 right now, unless you have a proper version of Weld too. At least a Google seems to say as much.
I am using Glassfish 4.0. Again the whole flow works well, I just can't seem to enter the flow using a navigation rule.
I would file a bug then.
If you use a navigation case then the NavigationHandler will lookup for a direct match of the <to-view-id> element. If there is one it will not start a new flow unless you define a <to-flow-document-id /> element. Thus the flow context is not initialized.
The most time the flow document id is not defined so it will be empty. But you still need the element in the navigation case. Because the NavigationHandler uses the outcome to determine the flow you need to use the flow-id as outcome for the navigation rule. Since the flow call overwrites the normal navigation the <to-view-id> is not used and the value doesn't matter (but there must be one).
In this case the only advantage of using the navigation rule is that you can use redirect=true.
The first page in the flow is defined as <start-node> in the flow definition. If there is no <start-node> the view with the id of the flow name is called.
If you enter a flow you can't choose the start page individually.