Reason for warning "avr:build doesn't define a 'build.board' preference" when build.board is explicitly set in boards.txt? I am trying to set up a custom board under the Arduino IDE, but I can not figure out why I am getting the warning...

Warning: Board Move38:avr:build doesn't define a 'build.board' preference. Auto-set to: AVR_BUILD


I think am following the recommendations and template in the official spec here...
https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5-3rd-party-Hardware-specification#boardstxt

My "vendor/maintainer" is move38 and my platform is avr, so the path to the boards.txt is...

Arduino\hardware\Move38\avr\boards.txt


Here is my boards.txt that defines the blink board...

blink.name=Blinks Tile
blink.upload.tool=avrdude
blink.upload.protocol=avrisp
blink.upload.maximum_size=15872
blink.upload.maximum_data_size=1024

blink.build.core=blinks
blink.build.board=AVR_Blink

blink.build.mcu=atmega168pb

blink.c.extra_flags=-Wextra -flto
blink.c.elf.extra_flags=-w -flto
blink.cpp.extra_flags=-Wextra -flto
blink.ltoarcmd=avr-gcc-ar

# set F_CPU to 1Mhz for all boards on this platform
build.f_cpu=1000000L


...which would seem to define build.board as AVR_BLINKS.

I think am following the recommendations and template in the official spec here...
https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5-3rd-party-Hardware-specification#boardstxt

...but nonetheless the warning persists. 

I am using Arduino IDE version 1.8.3 on Windows. 

What am I missing here? Is there something special about the value, format, or position of the build.board key that I am missing here?

Thanks!

More notes

Adding the following lines to a working boards.txt file...

build.name=testname
build.f_cpu=4000000L
build.core=blinks
build.board=AVR_BOARD


Will create a menu entry for a new phantom board called testname, but this is not a real board with usable keys. If you compile while that board is selected, you get the warning...

Using board 'build' from platform in folder: C:\Users\passp\Documents\Arduino\hardware\Move38\avr
Using core 'arduino' from platform in folder: C:\Users\passp\Documents\Arduino\hardware\Move38\avr
Warning: Board Move38:avr:build doesn't define a 'build.board' preference. Auto-set to: AVR_BUILD


...despite the fact that the key build.board is explicitly defined.
It appears that you can no longer set a global property in the boards.txt file. You must set every property individually inside each board ID, even if they are the same for every board in the file. This seems to contradict the documentation that states that...


  The other properties will override the corresponding global properties
  of the IDE when the user selects the board.


Further, if any global key is set directly, then both the board specific keys  and the global keys are ignored.

So in my above boards.txt, setting the the global key build.f_cpu at the end of the file seems to cover the blink.build.board key and prevent it from being copied to build.board when the board is selected. Even if you set the global key build.board directly, this setting is ignored.