Governing Magazine has a very good article by Alan Ehrenhalt on the problems that occur when the black robes get involved in redistricting. He writes in part that :
After more than three decades, there is essentially no usable law on race and redistricting, or at least, no law that helps much in making decisions. Judges in a redistricting case can do just about anything their values and political prejudices urge them to do.
Ehrenhalt favors getting the judges out of redistricting, but prohibiting mid-decade redistricting.