I believe something like the following diff restores the previous behavior (untested!):

diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py
index a61c2b0..4a8f83e 100644
--- a/Lib/logging/__init__.py
+++ b/Lib/logging/__init__.py
@@ -129,7 +129,7 @@ def getLevelName(level):

     Otherwise, the string "Level %s" % level is returned.
     """
-    return _levelToName.get(level, ("Level %s" % level))
+    return _levelToName.get(level, _nameToLevel.get(level, ("Level %s" % level)))

 def addLevelName(level, levelName):
     """