HP 300-019 HDMI video won't come back after display put to sleep

Hello,

I'm in the process of trying out this little machine and one major problem is that the video signal won't come back after the display is put to sleep. If I walk away for 20 minutes, come back, the display is off, and under normal conditions, I should be able to get the signal back by moving the mouse or pressing a key on the keyboard. But nothing. I can hit CTRL+ALT+F1 and get a text console, so the system is not frozen, merely tty7 is not able to restore the graphical session.

I can get a new graphical session by typing "sudo service lightdm restart".

$ sudo lshw -class video
[sudo] password for adam: 
  *-display               
       description: VGA compatible controller
       product: Haswell-ULT Integrated Graphics Controller
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 0b
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:48 memory:f6c00000-f6ffffff memory:e0000000-efffffff ioport:f000(size=64)