Test 8 submits a VAR_LOGIC expression that the derived-variable scan refuses, so the child is expected to abort and the assertion reads its message from the response. Without failfast=0 mpe_execute aborted this program instead, so the case could never reach its assertion. The file's other abort-expecting calls already pass failfast=0. This does not make the case pass on its own - the child still cancels without writing a response, which is tracked separately - but it removes the wrong failure in front of it.