:returns: A list of block matches which appear to differ

def differing_blocks(self):
        """
        :returns: A list of block matches which appear to differ
        """
        differing_blocks = []
        for (block_a, block_b) in self._block_matches:
            if not self.blocks_probably_identical(block_a, block_b):
                differing_blocks.append((block_a, block_b))
        return differing_blocks