When EHang Holdings Ltd. first sold shares to the U.S. public in December 2019, investors weren’t exactly sold on the rare chance to bet on the future of flying cars. The Chinese company makes "electric vertical take-off and landing” (eVTOL) aircraft, which function a bit like a helicopter but are powered by batteries and have multiple rotors. Its passenger drones are pilotless, too, unlike those of most of its rivals.

EHang’s listing — a traditional initial public offering underwritten by Morgan Stanley and Credit Suisse — raised just $41 million and valued the company at less than $700 million. Since then it has been caught up in a surge of excitement about the development of air taxis, and at the start of this week it was worth $6.8 billion.

On Tuesday its share price suffered a serious malfunction. More than 60% of its value went up in smoke after a short seller, Wolfpack Research, published a report questioning EHang’s sales relationships, technology and regulatory approvals. EHang said the report contains "numerous errors, unsubstantiated statements, and misinterpretation of information.”