Watch paired to chest strap but still using wrist sensor?

So my Forerunner 945 LTE is paired with my HRM Pro chest strap. My understanding is that the watch should now be using the chest stram HR data and not the wrist-sensor HR data (as long as my chest strap is actually on, which it is as I write this). However, I still see those green LEDS going at the back of the watch. Also, when I take the watch off my wrist, it stops showing heart rate even though I'm wearing my HRM Pro and the watch is showing the HRM Pro as connected.