When a player relocator is used on sand/gravel/other falling block, it does not replace one of the blocks. This was reported by Vaygrim on the IRC. Not really sure if more information is needed, if so, I can post. The assumption is that it doesn't copy the block due to it already not being there (falling sand entity).

Correction: Player relocator does return all the blocks, but the block under the falling sand stack will be deleted and replaced with one of the falling sand entities.