Since the most recent update any incoming calls don't pause media when the phone is on silent. It always used to.
If it's on either vibrate or sound mode then it does alert - but I have my phone on silent as a choice.
Up to this point it has always paused any playing media when a call would come in.
I've spoken to Samsung Support and they say it's not a setting I can change - it's standard functionality that calls should take precedent so it's potentially a bug.
I've already reset my phone to no avail - so I'm wondering if anyone else is having the same issue so it can definitely be reported as a bug.