The Bug:

Channeling doesn't affect mobs in some circumstances, here's a list of what i tested:

~~slabs~~	~~not struck by lightning bolt~~
~~stairs~~	~~struck by lightning bolt when mob is standing on the upper half;~~ ~~not struck if standing on the lower half~~
soul sand	not struck by lightning bolt
~~farmland~~	~~not struck by lightning bolt~~
~~grass path~~	~~not struck by lightning bolt~~
snow	not struck if snow layers is 8
Mob in a boat	not struck by lightning bolt. This doesn't affect passive mobs.
Mob in a minecart	not struck by lightning bolt. This doesn't affect passive mobs.
Honey block	not struck by lightning bolt
Inside a cobweb	not struck by lightning bolt
Inside lava	not struck by lightning bolt
Inside water	not struck by lightning bolt
Inside Powder Snow	not struck by lightning bolt

Note: Mobs riding horses are not affected.

Channeling doesn't affect mobs standing on some non-full blocks and in boats/minecarts