Following up on this post, see this Atlanta Journal-Constitution article. Still very curious:

Spokesmen for the Justice Department did not return calls for comment or to explain why the system was granted preclearance.
Lawyers for two groups who joined the lawsuit would like that explanation.
“It came as something of a shock,” said Laughlin McDonald, the voting rights project director for the American Civil Liberties Union.
Jerry Gonzalez, executive director of the Georgia Association of Latino Elected Officials, said the decision raises many questions.
“This is completely out of line for what the normal procedures are for preclearance,” Gonzalez said. “There was no time for public comment or engaging of impacted communities in the preclearance effort.”