Loading files from data packs and sounds ignores sub folders (causing e.g. no sounds at all in 17w43a)

As the title states:

[17:05:01] [Server thread/ERROR]: Couldn't read function medabots_server:stagerunsnowfield_a_second_go from medabots_server:functions/stagerunsnowfield_a_second_go.mcfunction

the file is actually located in medabots_server/functions/stage/run/snowfield_a_second_go.

The files simply do not load if they are in a sub folder, regardless of whether they are valid or not.

This is the case for:

• Advancements (Custom packs only)
• Loot tables (Custom packs only)
• Functions (Custom packs only)
• Sounds (Vanilla only)

In the case of sounds, this produces error messages like these, for all of the sound events in the game:

Missing sound for event: minecraft:ambient.cave
Missing sound for event: minecraft:weather.rain.above