"System setting" checkbox cannot be checked/unchecked if no other setting is changed

Steps to reproduce :

1)edit an existing network manager openvpn connection
2)check or uncheck the box marked "system setting"
3)validate
4)reedit the same connexion

Expected result :
The "system setting" box is checked or unchecked according to 2)

Actual result :
The modification has not been saved

Note :
It is possible to save the modification by changing some other setting