I know this issue has already been raised before, but I still can't find the definite, official answer from the core team on why block permissions defined in Page Type Defaults don't propagate to blocks already on pages.

I mean, those pages have "Assign Permissions: From Page Type Defaults" set, and the message "This block is an alias of Page Defaults. Editing it here will 'disconnect' it so changes to Page Defaults will no longer affect this block." is displayed for the block in question. In my understanding, such message should imply that edits made in Page Type Defaults should still "affect" the descendant blocks, isn't it logical? Otherwise it's confusing. What makes them still "connected" if in fact they are not?

In my eyes, it rather looks like a bug or a huge inconvenience, not a feature. Observed in 5.6.1.2. What's your opinion?

Moreover, any edits made by content editors on pages to the CONTENT of the block effectively disconnect it from its prototype on Page Type Defaults. Again, I consider it a major flaw. This means that there is no way to control permissions "from a central location". Once pages are created and edited, we can no longer change permissions for blocks. We must either go through all pages and adjust permissions, or use Setup on Child Pages to first REMOVE all blocks, lose their content, and then to re-add block on pages, losing the order of blocks in the Area. If that's not a major flaw in the permission system, then I don't know what is :)

Please share your thoughts, or correct me if I misunderstand something.