I've seen the following problem in two Motorola Moto Gs.
I disliked the inbuilt dialer from Android 4.4, so I put a custom dialer instead.
First time it asked me what app I want to use for dialing. I've selected the custom dialer and I've selected the ALWAYS option.
But, when I have a missed call and I want to call back that number from the notification bar, it still ask me what dialer should I choose. Everytime.
If I disable / freeze the inbuilt caller, I can't receive calls.
So, do you have any suggestions?