I think this started since I received the last upgrade.
I'm on a call on speakerphone. Another call comes in and on the first ring it takes my existing call off of speakerphone. I press speakerphone button and the call is back on speakerphone. It doesn't hang up; it just takes it off of speakerphone. Same thing happens when I'm on bluetooth headset. Happens every time. I can't believe I can't find an existing thread on this.
Samsung SCH-I535
Android 4.1.2