Microsoft CEO Satya Nadella sold more than half his shares in the Redmond tech giant last week in a $285 million transaction that some suspect was timed to escape a market downturn and lower Nadella’s exposure to a looming capital gains tax in Washington state.

Nadella sold the 838,584 shares on Nov. 22-23, according to company filings with the federal Securities and Exchange Commission. In a statement Tuesday, a Microsoft spokesperson said Nadella sold the shares “for personal financial planning and diversification reasons,” and added that Nadella, who is also company chairman, “is committed to the continued success of the company and his holdings significantly exceed the holding requirements set by the Microsoft Board of Directors.”

The sale of stock, which appears to be by far the largest by Nadella since being named CEO in 2014, doesn’t seem to have been mentioned at Microsoft’s annual shareholder meeting on Tuesday, as the company fended off shareholder proposals related to workplace equity and other issues. Shareholders passed a proposal to strengthen policies on sexual harassment put forward after allegations of misconduct were made against Microsoft co-founder Bill Gates.

The timing of the sale, first reported Monday by The Wall Street Journal, has raised questions among some analysts.

Nadella may have wanted to minimize his liability under Washington’s new 7% capital gains tax, which goes into effect Jan. 1, as well as any new federal taxes now under discussion in Congress, said Ben Silverman, director of research at InsiderScore/Verity.

“Whether that was a motivator or not, I can’t speak to that,” Silverman said. But “it’s worth pointing out that the timing, coming about six weeks before the implementation of that [tax], is curious for a sale of this size.”