There are 2 obsolete scroll blocks block (x scroll) and (y scroll) that is used to be in alpha versions of Scratch 2.0 which is already inside the project, but it still reports undefined as it must report the position of the backdrop if the scroll backdrop blocks are used. Are the rest of the blocks back yet? If so, when the blocks (x scroll) and (y scroll) must not equal undefined, then it should be returned already, otherwise, if they still reports undefined, then they are still not back yet :(
