Pasting a URL of type: file:///C:/Users/diaza/Desktop/model.doc/wms_m.html#robo81 into a node is interpreted (i.e. opened in the web browser) as C:/Users/diaza/Desktop/model.doc/wms_m.htm , with no hashtag. This prevents opening a webpage at a desired location in the scroll space.
This is not a yEd problem, but a shortcoming of the browser you use.
See also yED cuts anchor information in the URL-Field of the properties\data tabulator in the case of using "file:/"-uri.