diff --git a/9_Firmware/9_3_GUI/radar_protocol.py b/9_Firmware/9_3_GUI/radar_protocol.py
index a3f71b1..76c7342 100644
--- a/9_Firmware/9_3_GUI/radar_protocol.py
+++ b/9_Firmware/9_3_GUI/radar_protocol.py
@@ -679,16 +679,26 @@ class DataRecorder:
     def record_frame(self, frame: RadarFrame):
         if not self._recording or self._file is None:
             return
+        # GUI-S2: snapshot the arrays before handing them to h5py. The same
+        # frame object is also queued for the display consumer, and h5py
+        # releases the GIL during gzip compression — without this copy, any
+        # in-place mutation by the consumer (or a future scaling/normalization
+        # step) would tear the on-disk frame.
         try:
+            mag  = np.asarray(frame.magnitude).copy()
+            rdi  = np.asarray(frame.range_doppler_i).copy()
+            rdq  = np.asarray(frame.range_doppler_q).copy()
+            det  = np.asarray(frame.detections).copy()
+            rprf = np.asarray(frame.range_profile).copy()
             fg = self._grp.create_group(f"frame_{self._frame_count:06d}")
             fg.attrs["timestamp"] = frame.timestamp
             fg.attrs["frame_number"] = frame.frame_number
             fg.attrs["detection_count"] = frame.detection_count
-            fg.create_dataset("magnitude", data=frame.magnitude, compression="gzip")
-            fg.create_dataset("range_doppler_i", data=frame.range_doppler_i, compression="gzip")
-            fg.create_dataset("range_doppler_q", data=frame.range_doppler_q, compression="gzip")
-            fg.create_dataset("detections", data=frame.detections, compression="gzip")
-            fg.create_dataset("range_profile", data=frame.range_profile, compression="gzip")
+            fg.create_dataset("magnitude", data=mag, compression="gzip")
+            fg.create_dataset("range_doppler_i", data=rdi, compression="gzip")
+            fg.create_dataset("range_doppler_q", data=rdq, compression="gzip")
+            fg.create_dataset("detections", data=det, compression="gzip")
+            fg.create_dataset("range_profile", data=rprf, compression="gzip")
             self._frame_count += 1
         except (OSError, ValueError, TypeError) as e:
             log.error(f"Recording error: {e}")
diff --git a/9_Firmware/9_3_GUI/test_GUI_V65_Tk.py b/9_Firmware/9_3_GUI/test_GUI_V65_Tk.py
index beee48b..8e1d0cc 100644
--- a/9_Firmware/9_3_GUI/test_GUI_V65_Tk.py
+++ b/9_Firmware/9_3_GUI/test_GUI_V65_Tk.py
@@ -425,6 +425,49 @@ class TestDataRecorder(unittest.TestCase):
             mag = f["frames/frame_000001/magnitude"][:]
             self.assertEqual(mag.shape, (NUM_RANGE_BINS, NUM_DOPPLER_BINS))
 
+    @unittest.skipUnless(
+        (lambda: (
+            __import__("importlib.util")
+            and __import__("importlib").util.find_spec("h5py") is not None
+        ))(),
+        "h5py not installed"
+    )
+    def test_record_frame_isolates_from_post_call_mutation(self):
+        # GUI-S2: the recorder must snapshot the frame's arrays so a
+        # consumer (or future in-place scaling) mutating the same RadarFrame
+        # after record_frame returns cannot tear the on-disk record.
+        import h5py
+        rec = DataRecorder()
+        rec.start(self.filepath)
+
+        frame = RadarFrame()
+        frame.frame_number = 42
+        frame.timestamp = 123.456
+        frame.magnitude = np.full((NUM_RANGE_BINS, NUM_DOPPLER_BINS), 7.0)
+        frame.range_profile = np.full(NUM_RANGE_BINS, 3.0)
+        frame.detections[0, 0] = 1
+        frame.range_doppler_i[1, 1] = 100
+        frame.range_doppler_q[2, 2] = -50
+
+        rec.record_frame(frame)
+
+        # Mutate every array in place AFTER recording — must not bleed into HDF5.
+        frame.magnitude.fill(0.0)
+        frame.range_profile.fill(0.0)
+        frame.detections.fill(0)
+        frame.range_doppler_i.fill(0)
+        frame.range_doppler_q.fill(0)
+
+        rec.stop()
+
+        with h5py.File(self.filepath, "r") as f:
+            fg = f["frames/frame_000000"]
+            self.assertTrue(np.all(fg["magnitude"][:] == 7.0))
+            self.assertTrue(np.all(fg["range_profile"][:] == 3.0))
+            self.assertEqual(fg["detections"][0, 0], 1)
+            self.assertEqual(fg["range_doppler_i"][1, 1], 100)
+            self.assertEqual(fg["range_doppler_q"][2, 2], -50)
+
 
 class TestRadarAcquisition(unittest.TestCase):
     """Test acquisition thread with mock connection."""