Yes it's normal and it depends on the security policy of your webhost.

Personnally I have a script that changes all permissions before autoupgrade and then secures the permissions again after upgrade.

Ok. Thank you François.
Two questions :
1/ why your special script is not a part of the install script ?
2/ What are then the good working permissions to reverse to ?
I did not took a list of the original settings - I know, it's stupid ;)
amitiés. Jacques

This is a server security policy matter that is outside the scope of the b2evolution PHP application.

1/ The special script can NOT be a PHP script. It heavily depends on the host you use.

2/ This completely depends on the hosting configuration you use.

Please see http://b2evolution.net/man/optimal-file-permissions for more info.

Thanks again.
Take care. jacques