Prevent CircularUKF state aliasing

src/pyrecest/filters/circular_ukf.py

@@ -245,7 +245,7 @@ def filter_state(self) -> GaussianDistribution:
     @filter_state.setter
     def filter_state(self, new_state):
         new_state = _as_circular_gaussian(new_state, "filter_state")
-        self._filter_state = new_state
+        AbstractFilter.filter_state.fset(self, new_state)
 
     # ------------------------------------------------------------------
     # Prediction

tests/filters/test_circular_ukf_state_ownership.py

@@ -0,0 +1,30 @@
+import unittest
+
+import numpy.testing as npt
+
+import pyrecest.backend
+from pyrecest.backend import array
+from pyrecest.distributions import GaussianDistribution
+from pyrecest.filters.circular_ukf import CircularUKF
+
+
+class CircularUKFStateOwnershipTest(unittest.TestCase):
+    @unittest.skipUnless(
+        pyrecest.backend.__backend_name__ == "numpy",
+        "mutable NumPy arrays required for aliasing regression",
+    )
+    def test_assignment_copies_state(self):
+        filt = CircularUKF()
+        assigned = GaussianDistribution(array([0.5]), array([[0.7]]))
+        filt.filter_state = assigned
+
+        self.assertIsNot(filt.filter_state, assigned)
+        assigned.mu[0] = 1.5
+        assigned.C[0, 0] = 2.0
+
+        npt.assert_equal(filt.filter_state.mu, array([0.5]))
+        npt.assert_equal(filt.filter_state.C, array([[0.7]]))
+
+
+if __name__ == "__main__":
+    unittest.main()