Re: wp and bp profile syncing–works only sporadically
The first way is for users that may have been registered before BuddyPress was installed. They can still login, post comments, and use the forums, but if they never edited their profile and set their display name(fullname), BuddyPress won’t find them.
The second is if a user edits their profile from the WordPress side (firstname, lastname, nickname) without changing their BuddyPress display name. At that point the two will be out of sync.
It’s possible to hook into the save profile action of WordPress and change the BuddyPress display name when the user changes their WordPress nickname, but some sites may want a combo of the firstname/lastname while others may want to use the nickname, and others still may not really even care or use either. From that perspective it makes sense to not have BuddyPress try to interfere too deeply with syncing profile fields that might not have a direct 1 to 1 relationship with each other.