The opening night of “©Murakami,” Takashi Murakami’s retrospective at the Museum of Contemporary Art in Los Angeles, outshone the standard high-­culture shindig. Luxury-goods giant Louis Vuitton, whose Murakami-designed purses, wallets, and scarves have helped propel the brand, subsidized the $1,000-a-plate gala. Kanye West performed, and the guest list—from Tobey Maguire to Christina Ricci—read like that of an Oscar-night fete. Outside, fireworks exploded.

At the exhibit, revelers shopped at a temporary Louis Vuitton boutique, the first of its kind, selling lv-monogrammed bags and wallets that had been Murakamied with squat-faced cartoon characters. That Vuitton had set up a retail shop in a ­museum was unusual enough, but equally notable were the artworks Vuitton was selling: 500 “limited-­edition” prints priced at either $6,000 or $10,000.

By any definition, sales were brisk. Hundreds of prints were snatched up by fans of the ­goateed artist. The trouble started when one of them, collector Clint Arthur, noticed that two of his Murakamis weren’t numbered, even though the accompanying certificates said they were. (Limited-edition works usually bear both the artist’s signature and a number to help establish authenticity and value.) The discrepancy was “a translation problem between Louis Vuitton and Takashi Murakami,” ­Arthur says a salesclerk told him.

But when Arthur wrote Murakami asking that the proper numbers be added, he received an answer from the legal department of Louis Vuitton North America. If Arthur was dissatisfied with his purchase, the letter said, he could return the artwork and be refunded his money plus interest.

But Arthur wanted to keep the pieces and have them numbered. Surfing the internet, he discovered a California law stating that dealers who willfully provide certificates of authenticity that contain incorrect information are liable for damages that total three times the cost of the print. He filed a class-action lawsuit against Vuitton, arguing that the company intentionally tried to pass off faulty documentation. While he was at it, Arthur slapped MOCA with a suit charging that the museum breached the same statute by selling Murakami prints without certificates in its gift shop.

In an attempt to smooth things out, MOCA has temporarily stopped selling the Murakami prints. But Vuitton maintains that it did nothing wrong and dismisses Arthur’s litigation as “baseless.” Meanwhile, the contretemps is prompting buzz in art circles. Auction executives say that Arthur has a point. “It’s a big deal if the accompanying certificate states that the print is numbered—say, 120 out of an edition of 150—and there is no matching number on the piece,” says Tudor Davies, the head of the print department at Christie’s. “It makes the certificate worthless.”

And it’s not just Arthur’s problem. According to his complaint, hundreds more of the prints were sold to unwitting buyers who assumed the certificates protected them. But without the promised numbers, those works could be worth 10 to 25 percent less on the secondary market. Indeed, when Santa Monica Auctions, located in Santa Monica, California, put one of the disputed Murakamis on the block in June, the reserve went unmet. “It’s a problematic piece,” says Robert Berman, the auction-house owner.

Some in the art business also raise the question of why Murakami, an experienced artist, wouldn’t number the prints. It’s not clear whether he left off the numbers by accident, whether he planned to make more of the prints and didn’t intend for Vuitton to sell them as numbered pieces, or if Vuitton produced the certificates without his knowledge. (Vuitton, like the salesclerk, says it was a translation issue. Murakami declined to comment.)

And it’s paradoxical that Louis Vuitton, a company so sensitive to having its own goods counterfeited, would end up involved in a case having to do with authentication. Intentionally or not, Vuitton sold something different from what was billed. Of course, the legal case against the company hinges on intent; in order for Vuitton to be held liable, Arthur will have to prove that the luxury conglomerate purposely tried to mislead buyers, rather than merely failed to notice that the pieces didn’t carry the requisite numbers.

At the very least, it seems, the company figured out that something was wrong somewhere along the line. When the Murakami show and the Vuitton boutique moved to the Brooklyn Museum in April—before Arthur’s lawsuit was filed—the certificates of authenticity had been edited and the promise of a numbered print deleted. For the show’s October move to the Museum für Moderne Kunst in Frankfurt, there will be no Vuitton boutique at all. As to the possible reason, both the Moderne and Louis Vuitton declined to comment.