Let's see if I can throw some light on the subject ...
I've noticed that there are editable contacts that come from your SIM, your agenda Gmail, Outlook, etc., etc., however, there are other times that you want to delete a contact says "You can not delete contacts accounts read-only. You can only hide. " These contacts correspond to the programs added as WhatsApp, Facebook, as to synchronize, they detect if your contact has the application and if so, is added as Unknown (green box with white pawn) in the case of WhatsApp or Facebook (blue box with white F) for FaceBook ...
If on the other hand you try to edit them, you say in the case of WhatsApp "Unable to edit SNS contacts on the phone" and this is because they are read-only records.
Indeed if you try to delete them tells you that stay hidden rather than deleted, but if you uninstall the program, I guess disappear, or whether the reference is reassigned WhatsApp again, it becomes visible and read-only.
That's the conclusion I've come too after making a thousand and one evidence. However, there are still things I do not understand: as I said above, if "display options" disable phone contacts from gmail, facebook, ALL of whassap ... of even a few contacts I keep coming on the list: some of facebook (from among the many that I have only one), some mail (few) and one that I think does not exist anymore because I have changed in gmail. That's what I can not find any explanation. Where do they keep those contacts ?? Some are displayed to facebook and facebook with her picture and all !! And what about the rest of facebook? Why some and not others? And of those few who leave or yes and that will not let me edit or delete or anything between them have nothing in common. Not all belong to any single application.
Therefore, I do not think it is worrying that remain in limbo and I think we can stay calm and to know which reference these messages. ¿No ??
For me this is an unfathomable mystery ... maybe a 'bug'? A "lock" that gave with so much change / update? I do not know. So that specific applications are blocked as "read only" to his contacts, I can understand, but I think it gives more problems than benefits, but the other did not understand and I also quite annoyed, because it does not rely on my book contacts. Have contacts around swarming "uncontrolled", appearing magically and without being edited ... For example, I have to compare facebook, gmail, WhatsApp and others to see if they are all that should not lack me anyone? Are they after tomorrow? Do I have to have people with outdated data profiles associated with other current contacts 'forever and ever'?