What should happen:

Loading and saving structures from a structure block is supposed to use the path ".minecraft/structures".

What actually happens:

The structures are loaded from and saved to the "saves/worldname/structures/" folder which doesn't exist and doesn't get created upon saving.

How to fix ?

In the auj class (as of 15w33b, contains only methods for loading and saving structure files), the only String field (b as of 15w33b) should have the value "structures" as in the default constructor.