There is a workaround, if you get hit by that bug.
But I’m not sure if it’s even necessary anymore. I had issues with that exact problem in the past, but I just flashed my phone again, get_unlock_ability set to 0 and at the point the device-flasher asks you to lock the bootloader, that flag was at 1 again. 
Still plenty of ways to 
it through other means, but if you follow the device-flasher, I think you should be fine.
The people who’ve been running custom ROMs with a locked bootloader for months now might have a different opinion 