In rare cases, a verified configuration may nonetheless incur an error on boot config (for example, T5300), due to an uncaught bug. If the user does not notice the error message on boot, the act of entering config mode, committing and saving will overwrite the failed config section. A warning to the user should be added in this case, on entering config mode. In addition, a check should be added to prevent the warning of 'unsaved' commits in case of boot config error, as this will be misleading (cf. comment in T5262).