With the Anniversary edition Win 10 upgrade, Defender was updated to work concurrently with many AV Programs. So what you are seeing is normal. To identify the Anniversary editions, your Win 10 build # will be 14393 or higher. If you're concerned about the performance impact of running two different real-time scanners, you can turn off real-time scanning on Defender and set it to do periodic (or scheduled) scans. You can also just disable it altogether. GPO is probably your best bet here but you could push out a registry change.
I have been running both concurrently with little to no performance impact.