Partial blocks usually ignore the "Editing their own talk page" checkbox on Special:Block (see https://www.mediawiki.org/wiki/Help:Blocking_users#Blocking for full details), so this checkbox is normally disabled for partial blocks.
Users without JS, and users creating blocks via the API, can choose this option with partial blocks, but it won't be enforced. However, Special:BlockList, Special:Log/block etc. will incorrectly report "cannot edit own talk page" in these situations. (See also T224032#5210078)
These lists should be consistent with how the block is enforced, not how it was created.
ipb_allow_usertalk should be saved as false only when:
- A block is sitewide
- A block is partial and there is a restriction on the User_talk namespace
If a user tries to save ipb_allow_usertalk in a way that does not conform with those rules, an error message should be shown and the block should not be saved.