I was having this problem as well, and it seems to be worse when the CPU usage is high or when I receive a notification of some sort. I was able to fix the problem by tweaking one of the settings in my custom kernel's governor settings, namely disable_hotplugging_media. I am using KT kernel on LiquidSmooth 3.0 and I thought it was a ROM/kernel issue, although it seems that people on stock are experiencing similar things, so the problem may be with Poweramp
SwiftKey keyboard shows over the Poweramp lock screen, if the keyboard was open before the screen was turned off. This makes it so that the keyboard needs to be swiped out of the way before the lock screen controls can be used. I am running Poweramp 2.0.9 build 550, Full Version, on a Samsung Galaxy S4. The Android version is KitKat, 4.4, from a custom ROM, LiquidSmooth 3.0. Any help or pointers are appreciated.