This issue persists, including in the latest released v7.8 stable version.
/system/leds/settings> print
all-leds-off: immediate
v.7.12, I have the same problem
Does anyone have a solution ?
Black electrical tape 1-2 layers 
Close the cabinet door?
Leds in the back can be disabled.
Turn around the device then ?
Closing cabinet door dims all leds (front and back) in a quickly-reversible way. 
…and at the same time kills radio signals, mr radio engineer
Oh, since when does this minor detail matter? I thought that turning off LEDs is THE thing and the rest doesn’t matter?
I used to keep a RB951G inside a hard-wood (oak) under-TV cabinet and wireless worked just fine in the same room with cabinet doors closed (signal strength around -60dBm at my chair). My better half loved it. Then some of younger members of household required wifi coverage in the bathroom … now there’s an Audience placed on top of book shelf. Its LEDs don’t bother me, book shelf has a few cm high “fence” around the top and Audience nicely sits behind it. So no need to use two layers of white tape to cover them. Signal is so strong that I fear getting radiation burns, but bathroom has got plenty of wifi signal