I've had a similar problem on my Samsung Galaxy Player 5.0 . When I minimize/run the app in the background the track I am playing will completely stop playing and does not resume from the previous position when re-started. The app does not crash but the audio stops and position re-sets to 0.
It seems to be linked to notifications and/or actions of other apps and only seems to happen when my device is asleep or the app is running in the background. I was running GoneMad with Runkeeper at the time.
That being said, I am also using a custom ROM which also recently had an update, which I still need to apply.
Right now I am running the following:
Android Version: 4.2.2
Kernel: Sultan Version 3.5
The Rom is Called PAC and is based off of a combination of Cyanogenmod 10.1, AOKP mr1 Build 1 and ParanoidAndroid 3.15
I will update the ROM later today and see what happens. There is also a newer version of the Kernel I am using however, there is a problem with USB Mass Storage in the newer versions so, I am waiting on something more stable before I update.
If the updates do not resolve the issue I will use CatLog and see what I can find.