Breaking long grass and then continuing to break the grass it was on without releasing the mouse click allows the block to be mined, but it will reappear directly after breaking without giving a block. Using a tool decreases the durability of the tool which can be seen by mining the same block repeatedly. This durability is restored upon breaking a different block.

*What I expected to happen was that I would break the long grass and then mine the grass block without ending the mousclick
*What happened was the block reappeared repeatedly after mining it until the mouse click was released.

*UPDATE*
Also works with other non-solid block/solid block combinations, for example breaking a torch and then mining a fence post.