It's not always happen, but usually. After making calls, my screen is like flashing with black color (it's like losing connection with the screen). As i notice, longer the call i make, the stronger it'll flash, it's like the black flash area is larger than the fine area. Locking screen and restarting won't help, but it stop by itself slower and slower until all the area is fine. I don't know what it is. It's hard to tell and I don't have other device to record (i can post to all of u when I borrow my friend's phone to record if u guys want). It happens since I use first firmware, Amber and now Black.
If anyone ever face this problem pls tell me. And I hope it's not gonna kill my phone in the future, because I'm going to hold this phone for very long until i get a brand new one ( u know, money...). Sorry for my English, not my native.