Some schematics don't seem to load properly, while others work just fine. I tested a few schematics, and it seems like .schematics and .litematics don't work while .schems do work.
Examples
TestedSchematics.zip contains the schematics I have tested.
1 and 2 work fine. 1:

In 3 and 4, all blocks have suddenly become air. Screenshot of code (offset returns 0,0,0):

5 outputs a bugged schematic that somewhat looks like what it should look like, but obviously it is not 100% correct.

Hope you can do something with this.