Win10 Fall Creators Update - 3 of 4 monitors fail to sleep

With a four monitor (2x2) Eyefinity display group, after installing the Windows 10 Fall Creators Update, only the designated main display will now enter power saving mode (sleep).  Prior to the update, all monitors entered sleep mode simultaneously, with all 4 displays off and the display power button LEDs slowly blinking (indicating sleep status).  Now, only the main display sleeps as before.  The other three monitors go blank but not off, and the displays' backlights and power button LEDs stay on continuously.  Is anyone else seeing this behavior?  Any solutions?

 

System:  Desktop, Windows 10 Pro 64-bit, v1709, Build 16299.19 (Fall Creators Update)

Graphics:  AMD HD7990, Radeon Crimson 17.7.1, without ReLive

Displays:  (Four)  Dell U2715H  (As an Eyefinity 2x2 display group:  5120 x 2880 @ 60 hz), individually cabled DisplayPort 1.2 connections

Motherboard:  ASRock X99 WS, BIOS P1.70

CPU:  Intel Xeon E5-1650v3

PSU:  SeaSonic Snow Silent 1050  (80+ Platinum)

RAM:  16GB