Cannot light the sides or bottom of infinitely-burning blocks on fire

Attempting to use flint and steel on the sides or bottom of blocks which support infinitely burning fire, such as netherrack, magma blocks and End bedrock, or on blocks which support soul fire, nothing happens. Attempting to force fire there by removing a supporting burning block will cause the fire to disappear. This means there is no way to have infinitely burning side-of-block fire, nor side-of-block soul fire.