San Francisco ? An estimated 18,000 same-sex couples who wed in California last year have some good news with a bitter twist: Their marriages are valid, but also legal anachronisms that the state would not sanction if they wanted to exchange vows today.

The door to gay marriage in California — opened by a California Supreme Court ruling last spring and closed by voters in November — stayed shut under a 6-1 ruling Tuesday by the high court. The justices refused to nullify marriages that took place before the ban was approved, but for the couples involved, relief was mixed with a sense of being marginalized.

“I feel very uncomfortable being in a special class of citizens,” said Sharon Papo, who married Amber Weiss on June 17, the first day gay marriage became legal in the state.

Newlyweds such as Randy Nadeau, 43, and Will Lawson, 47, didn’t know how to react.

“We’re celebrating. We made it. But we’re sad for everyone else,” said Nadeau, who wed his partner of 17 years two days before voters passed Proposition 8 in November. “In general, we’re just embarrassed that the gay capital of the U.S. couldn’t get it together.”

Rejecting a series of legal challenges to the gay marriage ban, the state’s highest court ruled that stripping gays and lesbians of the right to wed was a legal exercise of the virtually unfettered initiative power the California Constitution grants its citizens.

But the court also unanimously held that it would be unfair and unnecessarily disruptive to dissolve marriages conducted during the brief five months when same-sex marriage was legal in California.

Applying Proposition 8 retroactively would have the effect of “throwing property rights into disarray, destroying the legal interests and expectations of thousands of couples and their families, and potentially undermining the ability of citizens to plan their lives,” the court said.

With marriage remaining off-limits to same-sex couples for the foreseeable future, gay rights leaders decried the ruling as an empty victory. Demonstrators wept and yelled, “Shame on you!” and at least 150 people were arrested for blocking an intersection during a post-ruling demonstration.

In the Castro District, the hub of San Francisco’s gay community, the large rainbow flag that waves in Harvey Milk Plaza was lowered to half-mast and replaced with a black mourning stripe at the top.

“It is hard to imagine the court would have permitted any other group to be stripped of equality and excluded from marriage,” said Shannon Minter, who challenged Proposition 8 as legal director of the National Center for Lesbian Rights. “Five years from now, people will see this decision as an example of the court’s historical blind spot.”

Activists said they would take the issue back to voters as early as next year.

Attempting to repeal a constitutional ban on same-sex marriage at the ballot box “has never happened in this country, but we are going to do that in California,” said Geoffrey Kors, executive director of Equality California. He added that gay marriage proponents would need to ramp up their efforts quickly to submit ballot language to the state by September.

A federal lawsuit challenging the ban was filed Friday in San Francisco. Prominent lawyers Theodore B. Olson and David Boies filed it on behalf of two gay men and two gay women, arguing that Proposition 8 violates the U.S. constitutional guarantee of equal protection and due process.

Olson said he hopes the case, which seeks a preliminary injunction against the measure until the case is resolved, will wind up before the U.S. Supreme Court. He is a former U.S. solicitor general who served in high-level Justice Department jobs in the Reagan and George W. Bush administrations.

Proposition 8 proponents said they wouldn’t challenge the existing gay marriages that were protected by the state high court.

“We see it as really a minor point in ultimately the will of the people being upheld,” said Andy Pugno, general council for the Yes on 8 campaign who argued the case with former Whitewater prosecutor Kenneth Starr.