diff --git a/src/pyftms/client/backends/updater.py b/src/pyftms/client/backends/updater.py
index dc51867a09..7d322b625f 100644
--- a/src/pyftms/client/backends/updater.py
+++ b/src/pyftms/client/backends/updater.py
@@ -46,16 +46,24 @@ def _on_notify(self, c: BleakGATTCharacteristic, data: bytearray) -> None:
             _LOGGER.debug("'More Data' bit is set. Waiting for next data.")
             return
 
+        result = self._result.copy()
+        prev = self._prev.copy()
+
         # My device sends a lot of null packets during wakeup and sleep mode.
         # So I just filter null packets.
-        if any(self._result.values()):
-            update = self._result.items() ^ self._prev.items()
+        if any(result.values()):
+            missing = object()
+            update = {
+                key: value
+                for key, value in result.items()
+                if prev.get(key, missing) != value
+            }
 
-            if update := {k: self._result[k] for k, _ in update}:
+            if update:
                 _LOGGER.debug("Update data: %s", update)
                 update = cast(UpdateEventData, update)  # unsafe casting
                 update = UpdateEvent(event_id="update", event_data=update)
                 self._cb(update)
-                self._prev = self._result.copy()
+                self._prev = result
 
         self._result.clear()
diff --git a/src/pyftms/client/manager.py b/src/pyftms/client/manager.py
index a62dd8cc26..0fa664eac2 100644
--- a/src/pyftms/client/manager.py
+++ b/src/pyftms/client/manager.py
@@ -61,8 +61,8 @@ def get_setting(self, name: str) -> Any:
 
     @property
     def properties(self) -> UpdateEventData:
-        """Read-only updateable properties mapping."""
-        return cast(UpdateEventData, MappingProxyType(self._properties))
+        """Read-only snapshot of properties mapping."""
+        return cast(UpdateEventData, MappingProxyType(self._properties.copy()))
 
     @property
     def live_properties(self) -> tuple[str, ...]:
@@ -75,8 +75,8 @@ def live_properties(self) -> tuple[str, ...]:
 
     @property
     def settings(self) -> SetupEventData:
-        """Read-only updateable settings mapping."""
-        return cast(SetupEventData, MappingProxyType(self._settings))
+        """Read-only snapshot of settings mapping."""
+        return cast(SetupEventData, MappingProxyType(self._settings.copy()))
 
     @property
     def training_status(self) -> TrainingStatusCode:
diff --git a/tests/test_manager.py b/tests/test_manager.py
new file mode 100644
index 0000000000..769c51b8c2
--- /dev/null
+++ b/tests/test_manager.py
@@ -0,0 +1,44 @@
+from pyftms.client.backends import SetupEvent, UpdateEvent
+from pyftms.client.manager import PropertiesManager
+
+
+def test_properties_returns_stable_snapshot():
+    manager = PropertiesManager()
+    manager._on_event(UpdateEvent("update", {"speed_instant": 3.0}))
+
+    properties = manager.properties
+    iterator = iter(properties.items())
+    assert next(iterator) == ("speed_instant", 3.0)
+
+    manager._on_event(UpdateEvent("update", {"cadence_instant": 90.0}))
+
+    assert list(iterator) == []
+    assert dict(properties) == {"speed_instant": 3.0}
+    assert manager.properties["cadence_instant"] == 90.0
+
+
+def test_settings_returns_stable_snapshot():
+    manager = PropertiesManager()
+    manager._on_event(
+        SetupEvent(
+            event_id="setup",
+            event_data={"target_resistance": 5.0},
+            event_source="callback",
+        )
+    )
+
+    settings = manager.settings
+    iterator = iter(settings.items())
+    assert next(iterator) == ("target_resistance", 5.0)
+
+    manager._on_event(
+        SetupEvent(
+            event_id="setup",
+            event_data={"target_power": 120},
+            event_source="callback",
+        )
+    )
+
+    assert list(iterator) == []
+    assert dict(settings) == {"target_resistance": 5.0}
+    assert manager.settings["target_power"] == 120
diff --git a/tests/test_updater.py b/tests/test_updater.py
new file mode 100644
index 0000000000..2319582506
--- /dev/null
+++ b/tests/test_updater.py
@@ -0,0 +1,35 @@
+from pyftms.client.backends import DataUpdater
+from pyftms.models import IndoorBikeData
+
+
+class _FakeRealtimeModel:
+    def __init__(self, data):
+        self._data = data
+
+    def _asdict(self):
+        return self._data
+
+
+class _FakeSerializer:
+    def __init__(self, *payloads):
+        self._payloads = iter(payloads)
+
+    def deserialize(self, _data):
+        return _FakeRealtimeModel(next(self._payloads))
+
+
+def test_updater_uses_stable_snapshot_for_callback_event():
+    events = []
+    updater = DataUpdater(IndoorBikeData, events.append)
+    updater._serializer = _FakeSerializer(
+        {"speed_instant": 5.0},
+        {"cadence_instant": 90.0},
+    )
+
+    updater._on_notify(None, bytearray(b"\x00"))
+    first_event_data = events[0].event_data
+
+    updater._on_notify(None, bytearray(b"\x00"))
+
+    assert first_event_data == {"speed_instant": 5.0}
+    assert events[1].event_data == {"cadence_instant": 90.0}