Don't re-retrieve backend in session cm

qiskit_ibm_runtime/base_primitive.py

@@ -86,19 +86,10 @@ def _get_mode_service_backend(mode: Optional[Union[BackendV2, Session, Batch]] =
         raise ValueError("mode must be of type Backend, Session, Batch or None")
     elif get_cm_session():
         mode = get_cm_session()
-        service = mode.service  # type: ignore
-        try:
-            backend = service.backend(
-                name=mode.backend(),  # type: ignore
-                instance=mode._instance,  # type: ignore
-                use_fractional_gates=mode._backend.options.use_fractional_gates,  # type: ignore
-            )
-        except (AttributeError, TypeError):
-            backend = service.backend(
-                name=mode.backend(),  # type: ignore
-                instance=mode._instance,  # type: ignore
-            )
-        return mode, service, backend  # type: ignore
+        service = mode.service
+        backend = mode._backend
+
+        return mode, service, backend
     else:
         raise ValueError("A backend or session must be specified.")
 

release-notes/unreleased/2282.bug.rst

@@ -0,0 +1,4 @@
+Running jobs in a :class:`~.Session` or :class:`~.Batch` with
+a context manager and initializing a primitive without any parameters will reinitialize the
+Session/Batch backend. This could cause issues if the backend target has been modified so instead,
+the actual backend object is now used.