Permissions on regions seems to work for every group except the Default group in Permissions. I guess it's because Permissions doesn't create an entry fo users in default group.

Thx a lot for all those recent fixes.

Maybe same issue as https://github.com/sk89q/worldguard/issues#issue/37 ?

Can't tell, because I don't use the build flag.
Build flag is set to none on all my Regions and I simply add groups that I want to be able to build.
I wanted to ass group default to make a GueztZone, but it doesnt work. Not sure if its related with build FLAG

Well, my issue is not about the build flag in WGs regions, but in permissions (the plugin).
There is a build flag for every group, so you could set the default group to false, and they can't build anywhere, except in regions where they are owner/member and in regions where the build flag (that of WGs regions) is on allow.
Well, thats the way it should behave, thats why I opened the ticket. If that is working, you could make a "Freebuild" or "Guestzone" with also denying building everywhere else.
At the moment, everyone can build everywhere, except in defined regions where they aren't a owner/member or the (regions) build flag is on allow.