This is something really weird, I'll be listening to music, want to take a picture, open the lens, and it pauses my music. Pushing the camera button, and using the menu icon does the same thing. This is really irritating. As far as my experience has been with this phone, no other application does this, only camera, and minimizing, and reopening doesn't help. Is this a problem with the media player, or camera-ui? So my question is, how do I fix this, or stop this from happening, or is this a known bug that's being fixed, or will be fixed?

This is intentional policy and not a bug.
The media player adheres to the system's media resources policy. You may be able to work around it by using another media player that doesn't care about policies.

I would think from testing that, the stock camera-ui sends a signal to pause MAFW.
camera-ui2 from CSSU Testing does not do this.