My phone is on 7.1.2 and something I noticed recently was that in 7+ the phone automatically puts itself in Do Not Disturb when you are in a call. The problem is that regardless of what your settings are in Priority Mode, it blocks everything but the alarms. So it negates call waiting. I haven't found any setting to change this but I did find a workaround for it. Settings > Notifications > Phone App > Override Do Not Disturb
Obviously this means you can't use do not disturb properly if you want to block calls. Personally I don't and in those cases I just put the phone on vibrate.
On a side note I finally came around to using the context menus you can pop up off the home screen icons. Love the feature, have no clue what version they introduced that in.