spontaneous waking from sleep for a few seconds
Just received my 34UM95 a couple of days ago. Connected with Thunderbolt to my mid-2012 rMBP 15", which I'm using in clamshell mode. While it's a bummer that sound doesn't automatically switch to the external display's speakers and (moreso) that you can't control the volume from the Mac... Everything pretty much works fine within the limitations of this display (hopefully they'll get the sound output/volume issues resolved with a firmware update...note holding my breath).
My rMBP detects the display properly, without any hacks or tweaks, etc. Just shows up as a 34UM95 in the Display control, with correct resolution already set (Best for Display, 60Hz). I was worried about that as some users had stated the display was detected as a TV or had to apply a manual hack/config somewhere.
With that said: I do notice one annoying issue. I leave my display turned on and just let my rMBP go to sleep on its own, or put it to sleep. The LG goes to sleep and the power light blinks. Every once in a while (I think it's maybe once or twice per hour) the display comes to life with a "No signal. Entering power saving mode shortly" message...stays on for a couple of seconds then goes back to sleep. My desk is near my TV so I can see this happening while I'm watching TV. I assume it continues to do this (through the night, day, etc.) until I sit down and start using it again.
I haven't seen any reports of this bug. But then, I assume most folks are either 1) turning their displays off, 2) not hanging around their computers while they're sleeping, or 3) unplugging their Macbooks when done.
I don't recall my Apple Thunderbolt display (with the same rMBP) ever doing this. I thought I'd check in here. Maybe it is happening to other people too?
One theory I have is that it might be PowerNap mode sending a signal out across Thunderbolt...looking for peripherals or a network connection maybe?
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EDIT: Rats! Should have posted this in the MBP forum, although the bug probably applies to all Macs. Other thread is here:
https://forums.macrumors.com/showthread.php?p=19581829#post19581829