I tested this literally 5 minutes ago on my Samsung galaxy note 2 running Android 4.3.
Put birch logs as the ingredient in a furnace (top slot), then click oak logs. An oak log will be removed from your inventory and a birch log will be added to the ingredient slot of the furnace.
MCPE-66
Still an issue as of v0.7.5 alpha.
This is still an issue as of version 0.8.3 alpha.
I tested this literally 5 minutes ago on my Samsung galaxy note 2 running Android 4.3.
Put birch logs as the ingredient in a furnace (top slot), then click oak logs. An oak log will be removed from your inventory and a birch log will be added to the ingredient slot of the furnace.