UP2516D weird behavior after powerup from powersave mode

Dual-monitor setup with

1. NVIDIA GeForce GTX750 Ti
2. Dell UP2716D (DisplayPort, primary)
3. Dell UP2516D (HDMI, Secondary)

Power settings are configured to turn off the displays after 10 minutes, and that works fine.

Once in power-save mode, when I move the mouse or touch the keyboard the primary display turns on and shows the login screen.

Normally, after logging in the secondary monitor (UP2516D on HDMI) comes on.  Recently this behavior has changed, the display power is restored (the power light on the monitor is steady) but nothing is displayed.

Now here's the really weird part: I have discovered that all it requires is a very light touch on the monitor's bezel over the function buttons.  Just brushing my fingers over this area causes the display to light up.

I have double-checked all the connectors and confirmed that they are firmly seated, and experimented with touching other parts of the display and bezel.  Only a light touch over the function button area restores the display.

Is the monitor broken? What could possibly cause it to behave this way?