More bug 460020:  when F is a subclass of float, disable the unary plus
optimization (+F(whatever)).
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index e89f642..a50785f 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -1401,6 +1401,7 @@
     a = precfloat(12345)
     verify(float(a) == 12345.0)
     verify(float(a).__class__ is float)
+    verify((+a).__class__ is float)
 
     class madtuple(tuple):
         _rev = None