The abrupt departure on Wednesday of David Sokol, Warren Buffett’s heir apparent to take over management of Berkshire Hathaway, has raised eyebrows and caused the company’s stock to fall. At issue is Berkshire’s recent acquisition of Lubrizol Corp., a company in which Sokol apparently bought shares prior to his eventually successful pitch of the acquisition to Buffett.

As of 2:00 PM New York time Thursday, both the A and B shares of Berkshire Hathaway were down 2% in active trading, while the DJIA was up four points for the day and the S&P 500 was up a point. Lubrizol ’s shares were unchanged.

A New York Times report says that Sokol tendered his resignation abruptly on Wednesday, surprising not just Buffett but also those within Berkshire. Buffett said that he had spoken with Sokol the previous day and “received no hint of his intention to resign.” The report also quoted Buffett as saying the resignation was a “total surprise to me.” Sokol had tried twice previously to resign, and Buffett had successfully talked him out of it.

The suddenness of Sokol’s departure calls into question Berkshire’s pending purchase of Lubrizol, a company in which Sokol (left) held shares and which he pitched to Buffett as a potential target for acquisition. According to a Reuters report, Sokol purchased shares in Lubrizol prior to pushing it to Buffett, and the "Oracle of Omaha" mentioned that fact in the release announcing Sokol’s departure. He said that Sokol had bought shares in December, sold them, and then purchased more in January—quite a bit more, according to the report. The transaction has now raised eyebrows and raised the specters of possible insider trading and lack of transparency.

In that release from Berkshire Hathaway, sent in the form of a letter to shareholders on Wednesday, Buffett said Sokol's resignation had "surpised" him, and that "Neither Dave nor I feel his Lubrizol purchases were in any way unlawful." Furthermore, Buffett wrote that Sokol said the Lubrizol share purchases "were not a factor in his decision to resign."

Sokol's January purchase of 96,060 shares would bring him a profit of $2.98 million, according to the report, based on the share price during the days on which he purchased them—Jan. 5-7—and the price at which Buffett agreed to buy the company. Also, his abrupt departure after pushing the acquisition of the company, in which Buffett had no initial interest, has caused concern.

While some in the business defend his actions and say there was nothing wrong with his pitching the company to Buffett as one that he liked, others say that the issue is whether he benefited by inside knowledge of the transaction. Shares of Lubrizol have increased by 27% since the announcement of the deal, although it is still pending Lubrizol shareholder approval.

While Buffett has praised Sokol’s abilities and credited him with the turnaround of NetJets, a company with which he had no prior experience, Alice Schroeder, the author of The Snowball, a bestselling biography of Buffett, had pointed out that Sokol’s management style was tough and had upset employees. She also posted an email from Sokol to employees in which, she said in the report, he “threatened to shut down the company if people don’t stop criticizing him.”