diff --git a/repositories/plan/plan_postgres_repository.py b/repositories/plan/plan_postgres_repository.py
index aa1e30157..21540523a 100644
--- a/repositories/plan/plan_postgres_repository.py
+++ b/repositories/plan/plan_postgres_repository.py
@@ -26,8 +26,9 @@ class PlanPostgresRepository(PlanRepository):
 
     A re-run INSERTs a fresh Plan rather than deleting the prior one (the cascade
     delete was slow); when the new Plan is the default it demotes any prior
-    default Plan for the same (property_id, scenario_id) to ``is_default=False``,
-    so readers can select the current Plan via ``is_default=True``."""
+    default Plan for the same property — across all Scenarios — to
+    ``is_default=False``, so readers can select the property's one current Plan
+    via ``is_default=True``."""
 
     def __init__(self, session: Session) -> None:
         self._session = session
@@ -67,17 +68,17 @@ class PlanPostgresRepository(PlanRepository):
             return []
 
         # Demote prior default Plans for every property in the batch that is
-        # receiving a new default Plan — one UPDATE for the whole batch.
+        # receiving a new default Plan — one UPDATE for the whole batch,
+        # across ALL scenarios: readers select a property's default by
+        # portfolio + is_default alone, so the invariant is one default per
+        # property. Scenario-scoped demotion left a promoted first Plan
+        # (non-default scenario) defaulted forever alongside the default
+        # scenario's later Plan (#1490).
         default_pids = [r.property_id for r in requests if r.is_default]
         if default_pids:
-            # scenario_id is uniform per batch (one scenario per SQS message).
-            scenario_id = requests[0].scenario_id
             self._session.exec(  # type: ignore[call-overload]
                 update(PlanModel)
-                .where(
-                    col(PlanModel.property_id).in_(default_pids),
-                    col(PlanModel.scenario_id) == scenario_id,
-                )
+                .where(col(PlanModel.property_id).in_(default_pids))
                 .values(is_default=False)
             )
 
diff --git a/repositories/plan/plan_repository.py b/repositories/plan/plan_repository.py
index 149a88618..15cafced1 100644
--- a/repositories/plan/plan_repository.py
+++ b/repositories/plan/plan_repository.py
@@ -43,7 +43,8 @@ class PlanRepository(ABC):
     ) -> int:
         """Persist ``plan`` and return its Plan id. Keeps prior Plans for
         ``(property_id, scenario_id)`` as history; when ``is_default`` is True,
-        demotes those prior Plans to ``is_default=False``."""
+        demotes the property's prior default Plan — whatever its Scenario — to
+        ``is_default=False`` (one default Plan per property)."""
         ...
 
     @abstractmethod