From c830734535a2951d33548d0f0afb121950db6400 Mon Sep 17 00:00:00 2001
From: Matthias Alphart <farmio@alphart.net>
Date: Sun, 23 Aug 2026 22:33:00 +0200
Subject: [PATCH] Don't restore non-KNX attributes for KNX sensors (#179932)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
---
 homeassistant/components/knx/sensor.py |  4 +-
 tests/components/knx/test_sensor.py    | 64 +++++++++++++++++++++++++-
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/homeassistant/components/knx/sensor.py b/homeassistant/components/knx/sensor.py
index fe34dc2976fc..ba7f8b3fd9d2 100644
--- a/homeassistant/components/knx/sensor.py
+++ b/homeassistant/components/knx/sensor.py
@@ -181,7 +181,9 @@ class _KnxSensor(RestoreSensor, _KnxEntityBase):
             )
         ):
             self._attr_native_value = last_sensor_data.native_value
-            self._attr_extra_state_attributes.update(last_state.attributes)
+            # only restore KNX specific attributes - others may have changed
+            if (source := last_state.attributes.get(ATTR_SOURCE)) is not None:
+                self._attr_extra_state_attributes[ATTR_SOURCE] = source
         await super().async_added_to_hass()
 
     @override
diff --git a/tests/components/knx/test_sensor.py b/tests/components/knx/test_sensor.py
index 3557ae8f8167..7a18bce7a19b 100644
--- a/tests/components/knx/test_sensor.py
+++ b/tests/components/knx/test_sensor.py
@@ -12,8 +12,19 @@ from homeassistant.components.knx.const import (
     CONF_SYNC_STATE,
 )
 from homeassistant.components.knx.schema import SensorSchema
-from homeassistant.components.sensor import SensorDeviceClass, SensorStateClass
-from homeassistant.const import CONF_NAME, CONF_TYPE, STATE_UNKNOWN, Platform
+from homeassistant.components.sensor import (
+    ATTR_STATE_CLASS,
+    SensorDeviceClass,
+    SensorStateClass,
+)
+from homeassistant.const import (
+    ATTR_DEVICE_CLASS,
+    ATTR_UNIT_OF_MEASUREMENT,
+    CONF_NAME,
+    CONF_TYPE,
+    STATE_UNKNOWN,
+    Platform,
+)
 from homeassistant.core import HomeAssistant, State
 
 from . import KnxEntityGenerator
@@ -99,6 +110,55 @@ async def test_sensor_restore(hass: HomeAssistant, knx: KNXTestKit) -> None:
     assert not events
 
 
+async def test_sensor_restore_ignores_stale_attributes(
+    hass: HomeAssistant, knx: KNXTestKit
+) -> None:
+    """Test that restoring doesn't reapply attributes the entity doesn't provide."""
+    fake_state = State(
+        "sensor.test",
+        "ignored in favour of native_value",
+        {
+            ATTR_SOURCE: knx.INDIVIDUAL_ADDRESS,
+            ATTR_DEVICE_CLASS: SensorDeviceClass.POWER,
+            ATTR_STATE_CLASS: SensorStateClass.TOTAL_INCREASING,
+            ATTR_UNIT_OF_MEASUREMENT: "W",
+        },
+    )
+    extra_data = {"native_value": "42", "native_unit_of_measurement": None}
+    mock_restore_cache_with_extra_data(hass, [(fake_state, extra_data)])
+
+    await knx.setup_integration(
+        {
+            SensorSchema.PLATFORM: [
+                {
+                    CONF_NAME: "test",
+                    CONF_STATE_ADDRESS: "2/2/2",
+                    CONF_TYPE: "2byte_unsigned",  # no unit or device class
+                    CONF_SYNC_STATE: False,
+                },
+            ]
+        }
+    )
+
+    knx.assert_state(
+        "sensor.test",
+        "42",
+        **{ATTR_SOURCE: knx.INDIVIDUAL_ADDRESS},
+        device_class=None,
+        state_class=SensorStateClass.MEASUREMENT,
+        unit_of_measurement=None,
+    )
+    # a new telegram doesn't reintroduce the stale attributes either
+    await knx.receive_write("2/2/2", (0x00, 0x07))
+    knx.assert_state(
+        "sensor.test",
+        "7",
+        device_class=None,
+        state_class=SensorStateClass.MEASUREMENT,
+        unit_of_measurement=None,
+    )
+
+
 async def test_last_reported(
     hass: HomeAssistant,
     knx: KNXTestKit,