Use a custom exception to signal failure to reproduce (Low confidence).

scripts/slave/recipe_modules/auto_bisect_staging/local_bisect.py

Index: scripts/slave/recipe_modules/auto_bisect_staging/local_bisect.py
diff --git a/scripts/slave/recipe_modules/auto_bisect_staging/local_bisect.py b/scripts/slave/recipe_modules/auto_bisect_staging/local_bisect.py
index 9e6c3615a9080a19b08bc106ebbda58b97d7c4ba..0a511704a9f5ca98a9e6c8a6d50da2e107e3270f 100644
--- a/scripts/slave/recipe_modules/auto_bisect_staging/local_bisect.py
+++ b/scripts/slave/recipe_modules/auto_bisect_staging/local_bisect.py
@@ -35,10 +35,12 @@ def perform_bisect(api, **flags):
             continue
           else:
             raise
-  except bisect_exceptions.InconclusiveBisectException:
+  except bisect_exceptions.InconclusiveBisectException as e:
     if bisect_attempts:
+      bisect_attempts[-1].print_result_debug_info()
       bisect_attempts[-1].post_result()
-    raise api.m.step.StepFailure('Bisect cannot identify a culprit')
+    raise api.m.step.StepFailure('Bisect cannot identify a culprit: ' +
+                                 e.message)
   except Exception: # pylint: disable=bare-except
     if bisect_attempts:
       bisect_attempts[-1].post_result()
@@ -65,8 +67,6 @@ def _perform_single_bisect(api, bisect_attempts, **flags):
               bisector.bisect_over = True
         if not bisector.bisect_over:
           _bisect_main_loop(bisector)
-      else:
-        bisector.bisect_over = True
       bisector.print_result_debug_info()
       bisector.post_result(halt_on_failure=True)