Column AD_WF_Node_ID (which used in Start Node field) from AD_Workflow table shouldn't have an attribute Allow Copy. This can cause some problem which I'll describe below.
I've created new WF by copying the old record. Everything looks fine to me and I created nodes and transitions, including (Start) node. After testing I've encounted a problem - warnings in console for each node: "Added Node w/o transition:". Reason of this error, as you can guess - copied reference to node (Start) from another Workflow in Start Node field. It get through Dynamic Validation. Hard to realize problem when you have (Start) node almost in every Workflow.
Thanks for reporting, I think this issue was solved by