I wonder if the next step is getting rid of apostrophe and putting an end to the kingdom of proper names:

Zonguldağa gittim ama Karabüğü görmedim.

Come on si++, I can´t believe you ´don´t know the exact rule for that one´.

Come on scalpel, I don´t have to know everything. Turkish alphabet was designed to be a phonemic one and and we tend to write what we say as much as possible. I say we may see them "written as said" sometimes.

´Written as said´ thing is nothing but an urban tale. In this country only a very few say, for example, geliyorum by pronouncing properly all the letters, but we all have to write it as geliyorum,why?Even the official accent, İstanbul Accent, changed it to be said as geliyom. My problem is even worse: I say celiyrum and have to write it as geliyorum. 

Come on scalpel. If one says "geliyom" it is written as "geliyom". Otherwise how can you reflect it on the script? Suppose you are a script writer how you would you mention it on the paper? If it is to be said as "geliyom" you write it as "geliyom" or if "celiyrum" as "celiyrum". It is supposed be written (and said) as "geliyorum" is another matter. We are tought the standard Turkish and use it in official speech,but we also speak our local dialects sometimes. I both say "geliyom" in some places and "geliyorum" where necessary.

si++, in the first place, you owe me a "thank you" for changing the direction of the debate and saving you from sinking more and more into depression for k/ğ mutation in proper names.  In the second place, I must accept that you are a great demogog.  Finally,it´s no fun for me talking about any type of mutation.  

Let´s go to the fount of all wisdom: TDK

1. Aşağıda sıralanan özel adlara getirilen iyelik, durum ve bildirme ekleri kesme işaretiyle ayrılır:

a. Kişi adları, soyadları ve takma adlar: Atatürk’üm, Fatih Sultan Mehmet’e, Muhibbi’nin, Gül Baba’ya, Sultan Ana’nın, Yurdakul’dan, Kâzım Karabekir’i, Yunus Emre’yi, Ziya Gökalp’tan, Refik Halit Karay’mış, Ahmet Cevat Emre’dir, Namık Kemal’se.

UYARI : Sonunda p, ç, t, k ünsüzlerinden biri bulunan Ahmet, Çelik, Çiçek, Halit, Mehmet, Mesut, Murat, Özbek, Recep, Yiğit, Bosna-Hersek, Gaziantep, Kerkük, Sinop, Tokat, Zonguldak gibi özel adlara ünlüyle başlayan ek getirildiğinde kesme işaretine rağmen Ahmedi, Çeliği, Çiçeği, Halidi, Mehmedi, Mesudu, Muradı, Özbeği, Recebi, Yiğidi, Bosna-Herseği, Gaziantebi, Kerküğü, Sinobu, Tokadı, Zonguldağı biçiminde son ses yumuşatılarak söylenir.

i.e. It says although you say it like Dileğin you write it like Dilek´in.

Oh, I admit, püskevit was fun, but it is something different than mutation and, in my opinion, it is more a distortion, a funny one and I liked it!    

Yes, that´s what the rule says.

I was reading all the answers and I  truly appreciate your help and the Debate created here with the  k/g  mutation in this case !! Actually , it was not an easy or clear one even for turkish speakers or people who has more "technical" information related to grammar rules .Thank you MarioninTurkey  for the insight and to Si+ for your time and willingness to explain. Clear now. ¡Gracias! Thank you.