Asumption: There are two existing Parsrules which have the same class and namespace. Only the Elementname is different. Other Parserules which open Parsrules are working when the called Parse Rule has no duplicate in the same class with the same name space. This wrong behaviour is shown in the attached ppx File.
1. Make sure your test case is exactly the same for all your tests.
2. The DSS (when set it to true) should have the same behavior as that of pega 6 (which is working).
3. The fact that the DSS does not make any difference for 7.1.8 (confirm the same use case, and DSS is set correctly) is puzzling. If all the checks are done (use case/DSS set), this may be something else going on.