When using certain packs, elements of the mobile UI (such as within furnaces) are not rendered using the texture pack selected by the user.
I have found this issue to be present in the following packs:
Cartoon Texture Pack
Candy Texture Pack
Natural Texture Pack
Egyptian Mythology Mash Up
Norse Mythology Mash Up
Chinese Mythology Mash Up
N7 Mashup
Festive Mash-up 2016
Greek Mythology Mash Up
Vault-tec Mash Up
Dragonborn Mash Up
Halloween Mash Up
City Texture Pack
Plastic Texture Pack
Pattern Texture Pack
Steampunk Texture Pack
I have attached screenshots for reference
This issue is being tracked at MCPE-154347.