Android not remembering which music app was in use last when pressing headset play/pause button

My phone has developed an odd and hard to reproduce problem lately. I have been listening to a lot of audiobooks using BeyondPod. Throughout the day, I often pause and resume the tracks using the play/pause button on the headset. Usually this works without a hitch, but at random times it will launch the basic Android music player and start playing music, rather than resuming my audiobook where it was last paused. When I listen to music, I use Rocket Player. I have never intentionally launched the basic player. I used to have random conflicts between BeyondPod and Rocket Player, but after being told by the Rocket devs that they couldn't control which player got control if I had headset controls enabled in both players, I just started switching off the headset controls in Rocket Player when I wasn't using it. This worked for a while until recently when the basic player started launching instead. I have noticed that it seems to forget that I was using BeyondPod primarily if it has been paused for a while and other (non-music) apps have been launched. This leads me to believe that it is caused when BeyondPod gets deprioritized out of active memory. However, I have been unable to force it to make this switch on purpose. Is there any way to be able to select a system-wide default music player so it will stop launching the basic one? I couldn't find a setting for this in my phone. Alternatively, is there a way to mark an app as "higher priority" so it is less likely to be kicked out by other apps? Any other thoughts on solving this? ----- * Phone: Samsung Galaxy S4 (Sprint) * Android: 4.4.2 * Rooted, but on stock Samsung image.