diff --git a/jira/client.py b/jira/client.py
index e40d0948d..e8890538f 100755
--- a/jira/client.py
+++ b/jira/client.py
@@ -391,7 +391,7 @@ def add_attachment(self, issue, attachment, filename=None):
                 url,
                 files={
                     'file': (fname, attachment, 'application/octet-stream')},
-                headers=CaseInsensitiveDict({'content-type': None}))
+                headers=CaseInsensitiveDict({'content-type': None, 'X-Atlassian-Token': 'nocheck'}))
         else:
             method = 'MultipartEncoder'
 
diff --git a/jira/version.py b/jira/version.py
index 291636bee..557fae007 100644
--- a/jira/version.py
+++ b/jira/version.py
@@ -3,4 +3,4 @@
 # 1) we don't load dependencies by storing it in __init__.py
 # 2) we can import it in setup.py for the same reason
 # 3) we can import it into the jira module
-__version__ = '0.40'
+__version__ = '0.41'
diff --git a/tests/tests.py b/tests/tests.py
index bf03d3500..665eaa221 100755
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -386,15 +386,22 @@ def test_application_property(self):
             key='jira.lf.text.headingcolour')
         self.assertEqual(clone_prefix['value'], '#292929')
 
-    @unittest.skip("may fail to to running test concurrentlym")
     def test_set_application_property(self):
         prop = 'jira.lf.favicon.hires.url'
-        self.jira.set_application_property(prop, '/Tjira-favicon-hires.png')
-        self.assertEqual(self.jira.application_properties(key=prop)['value'],
-                         '/Tjira-favicon-hires.png')
-        self.jira.set_application_property(prop, '/jira-favicon-hires.png')
-        self.assertEqual(self.jira.application_properties(key=prop)['value'],
-                         '/jira-favicon-hires.png')
+        valid_value = '/jira-favicon-hires.png'
+        invalud_value = '/Tjira-favicon-hires.png'
+        counter = 0
+
+        while self.jira.application_properties(key=prop)['value'] != valid_value and conter < 3:
+            if counter:
+                sleep(10)
+            self.jira.set_application_property(prop, invalid_value)
+            self.assertEqual(self.jira.application_properties(key=prop)['value'],
+                             invalid_value)
+            self.jira.set_application_property(prop, valid_value)
+            self.assertEqual(self.jira.application_properties(key=prop)['value'],
+                             valid_value)
+            counter += 1
 
     def test_setting_bad_property_raises(self):
         prop = 'random.nonexistent.property'
@@ -1748,17 +1755,12 @@ def test_session_with_no_logged_in_user_raises(self):
         anon_jira = JIRA('https://support.atlassian.com', logging=False)
         self.assertRaises(JIRAError, anon_jira.session)
 
-    @unittest.skip("Returns AttributeError instead of ConnectionError due to serverInfo usage.")
     def test_session_server_offline(self):
         try:
             JIRA('https://127.0.0.1:1', logging=False)
         except Exception as e:
-            self.assertEqual(type(e), ConnectionError)
-
-            #@unittest.expectedFailure
-            # def test_kill_session(self):
-            #    self.jira.kill_session()
-            #    self.jira.session()
+            logging.error(e)
+            self.assertEqual(type(e), JIRAError)
 
 
 class WebsudoTests(unittest.TestCase):