It seems unlikely to me that Device Hub has anything to do with the capacitive buttons. For example I could even completely remove Device Hub and the capacitive buttons would continue to work.
I think someone just decided to "improve" the brightness of the capacitive buttons. They are now pegged at a brighter level than before. My main scenario for this device is to keep it on a nightstand and use it in the dark. The new brightness level is unacceptably bright and also drains the battery faster.
I have reverted to Cyan + DevPreview. Sigh.
I can't find the thread now... I could not find it earlier. I would link it if I could.
Someone found where Msft documented the behavior was linked to Device Hub. There was a workaround much more complex than a simple uninstall of Device Hub. Before I could use the workaround xandros9 stated in our Ambassador chat group that Msft had pushed an update to Device Hub that fixed it.
I had the blazingly bright capacitive buttons on Cyan...
The day xandros9 advised the fix was pushed my capacitive buttons were back to normal all on their own. Sure enough, Device Hub was at the bottom of my settings which indicates it was the last setting updated.
All this on Cyan and within the past week - I have yet to install Denim.
The Denim that was pushed was bundled prior to the Device Hub bug patch. Occam's razor suggests the old bug rode your OTA and a Device Hub update would have put your capacitive buttons back to normal. The chances that it is a brand new bug enacting previously observed behavior is a bit of a stretch...
Sorry you reverted for what may be no reason. I'm sorry I can't find the original citations. They are buried in the 1520 forum somewhere.