SLING-221 (Rev. 618697) code has been added to the SlingRequestDispatcher to cut off the servlet context path if the path to include has the context path as a prefix.
According to my reading of the Servlet Spec, the absolute path used to retrieve a RequestDispatcher is interpreted relative to the servlet context, that is the path is never prefixed with any servlet context path. Hence cutting of some piece of the path is not correct.
Note, that the assumption of cutting off the context path is used throughout a number of integration tests. These tests will fail and have to be fixed when fixing this issue.