You can read the opinion here.  A snippet:

Despite rhetoric of a “runaway plan,” the Court’s plan gave as much consideration to the State’s enacted map as possible without rubberstamping the districts that were the subject of legal challenges; this consideration was given to the enacted plans even though, as discussed below, a finding that a three judge court is required to apply Upham deference prior to a preclearance determination defies the plain language of the Voting Rights Act, the legislative intent behind Section 5, existing Supreme Court precedent, and a myriad of practical realities. Those practical realities include the Court’s obligation to ensure that the interim map does not contain split VTDs so that it is capable of being implemented under severe time constraints. This prevents the Court from adopting even the unchallenged districts from the enacted plan wholesale. Moreover, the Court is prevented from making Section 5 determinations not only because it lacks  jurisdiction to do so, but also because as a practical reality, the three judge panel has not heard evidence regarding Section 5; nor could it hear that evidence and make those determinations without wasting an enormous amount of judicial resources and potentially reaching a result that would later be inconsistent with a D.C. Court ruling.

A snippet from Judge Smith’s dissent:

This “Supplemental Opinion” has the smell of a brief on appeal. That is not the role of a trial court. It would be equally inappropriate for me now to point out the flaws in this latest submission.The talented attorneys on each side are fully capable of explicating the legal issues that will be considered, and if the Supreme Court needs further explanation from this three-judge district court, it will ask. If the majority feels insecure in the justification it gave in its initial offering, that is the stuff of appellate briefing by the parties’ attorneys, not judges and their law clerks. In my almost twenty-four years as a judge on the court of appeals, I cannot recall ever seeing an unsolicited “supplemental opinion” come flying over the transom from a district judge desperate to lend further support for a shaky decision. We are judges, not advocates.

The majority’s response in footnote 1:

1The dissent criticizes the issuance of this supplemental opinion as having “the smell of a brief on appeal.” The Court’s prior order expressly stated that a supplemental opinion would follow because the Court was unable to issue a full opinion under the severe time constraints. The sole purpose of this opinion is to provide a detailed explanation for how the Court drafted the interim House plan for the benefit of the parties, the Supreme Court, and future redistricting panels.