The title pretty much describes what's broken and how to recreate it.
To be more precise, to recreate this issue:
Use the newest version of Minecraft
Select a resource pack normally before joining servers or single player world.
Then the resource pack isn't loaded up.

A workaround:
Select your resource packs during the game.

More details:
The resource pack used while experiencing this bug was Programmer art.
When you have once started a single player world or joined a multiplayer server