404 error when editing transitions in an inactive workflow

steps to reproduce

1. Edit an inactive Workflow in the diagram mode;
2. click one of the transitions and try to access Properties, Conditions, Validators or Post Functions.

Result: 404 error "Oops, you've found a dead link."

This affects all inactive workflows, created from scratch and copied from active ones.

Workaround: use the Text mode of the editor, as it's not affected.