Prop 8 goes down as well. http://www.supremecourt.gov/opinions/12pdf/12-144_8ok0.pdf
The sequence of events was: a federal court struck down a California law (passed via Proposition 8), and California, rather than appealing the decision, said "ok" and accepted the ruling. That leaves no remaining live controversy between the State and the federal court system, so nothing for an appeals court to hear (says today's decision).
The decision was 5-4 but not strictly on ideological lines: 2 conservatives and 3 liberals in the majority, 3 conservatives and 1 liberal dissenting.
The assumption that the ideology of members of the court is unidimensional is not justified. "Not strictly according to the popularly perceived ideological factions of the court" is probably more supportable than "not strictly on ideological lines".