When creating a new keymap, if you enable VIA in the keymap's rules.mk and you set BOOTMAGIC_ENABLE to full, BOOTMAGIC_ENABLE works as 'lite'.
It's not a bug, it's a feature. 馃槀
Bootmagic Full is not as reliable as Lite, because it requires that the default layer upon startup contains, or allows access to, at least the space and B keys to get into bootloader mode. Lite, on the other hand, does not care which keys are mapped; it goes purely off of the switch matrix positions, and additionally clears the EEPROM. It's also a much simpler feature (= less code size) so I imagine we may at some point phase out Bootmagic Full, as there's not really that much need for all the extra bells and whistles it has.
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It's not a bug, it's a feature. 馃槀