How to make all the posts commentable by default? Imputs in Settings/Discussions are not saved

Question

I've modified my website quite a bit and now looks almost as I desire. I've set all the posts to be commentable in Settings/Discussions but it seems that this imput is not saved and new posts by authors are not commentable. Everytime, I need to "quick edit" the new post and mark the |_|Allow Comments field as selected |x|. This takes me a lot of time and I wonder if there's a way to have a function to make all the new posts as commentable as, just like I said, it seems not possible to choose it as option in Settings/Discussions.

Thanks!