NEW HAVEN, Conn. — Producers and presenters are scratching their heads trying to figure out how the last leg of the 10th anniversary U.S. tour of Matthew Bourne’s celebrated, stylish and unconventional “Swan Lake” turned into an ugly duckling.

The return of the modernistic ballet-theater spectacle — in which a sexually confused prince dreams of bare-chested male swans — started off with good numbers for its West Coast gigs. But as the show and its international cast of 38 headed East, “Swan” took a dive.

The Boston gig at the Colonial Theater in mid-April attracted “a little more than 50% houses,” says Drew Murphy, president of Broadway in Boston, which presented the show there. Things looked even worse for the remaining four cities.

On April 21, the tour was abruptly curtailed after playing seven cities, pulling the remaining dates at Washington, D.C.’s Warner Theater (April 25-30), Toronto’s Elgin Theater (May 2-7), Philadelphia’s Merriam Theater (May 9-11) and Baltimore’s Lyric Theater (May 12-14).

The tour began in January in Tempe, Ariz., before moving on to Minneapolis, Denver, Chicago and multiweek runs in Los Angeles and San Francisco.

“It’s very difficult to discern exactly what it is (when a tour runs into bad box office) after it plays well in other markets,” says producer Kenneth Gentry, CEO of NETworks Presentations, which presented the tour with Back Row Prods. in association with Bourne’s New Adventures. “You never really know. I believe marketing is like economics. It’s the furthest thing from an exact science.”

Still, the premature end of a touring vehicle once seen as a hot and hip show will keep industry insiders jawing for some time.

Was it the fact that in the canceled cities the show did not have the safety net of a Broadway subscription series, or even a dance series, which generally are smaller but still offer marketing advantages? Well, that wouldn’t explain how well it did in some cities where it was off-subscription.

Adding to Beantown woes was the cancellation of one of six perfs when technical difficulties forced Murphy to go onstage and tell the aud there would be no show. “Most of the people exchanged their tickets, and once word of mouth got out we started to do nice business.,” he says.

Spec on the whys of the tour’s closing also points to the difficulty of marketing a show that isn’t quite dance and isn’t quite legit. “Even though it appeared on Broadway, it’s not your typical Broadway show,” Murphy offers.

Some even raised the point that a decade after its provocative debut, a gender-bender ballet doesn’t have the buzz it once did; it was a sensation in London in 1995 and then opened in Gotham in ’98, winning three Tonys and running 124 perfs.

But that wouldn’t explain the strong numbers on the West Coast. Gentry says it’s possible that places where “Swan Lake” had played when it first came to the U.S. — such as Los Angeles’ Ahmanson Theater — had an advantage in terms of recognition.

“More and more it’s hard to get a branding for a production on a national basis — even shows that have played New York for years,” he says.

Gentry adds that since the cancellation happened in the final three weeks of the tour, the impact of the financial losses was “minimal. We recouped for this leg. There is just a longer-than-expected layoff.”

When asked how the “Swan Lake” cancellation might affect Bourne’s upcoming U.S. tour of his newest ballet, “Edward Scissorhands,” Murphy said the two shows are vastly different. The “Scissorhands” show should find a broader range of audiences because of the familiarity of the title, the popular Tim Burton/Johnny Depp film giving it “more mass appeal.”

Since “Swan Lake” premiered in the ’90s, Bourne has staged dance-theater pieces “The Car Man,” “Play Without Words” and “Cinderella” as well as choreographed Brit legit productions such as “My Fair Lady” and “South Pacific.” He returns to Broadway this fall as choreographer of Disney’s Brit import “Mary Poppins,” beginning perfs at the New Amsterdam in October.

As for “Swan Lake,” plans to continue touring internationally are still moving forward. “And I wouldn’t rule out us doing ‘Swan Lake’ here at a later time,” Gentry says.