In an era when partner mobility has become common place in Big Law, it’s only natural that some investments go south.

An announcement by Winston & Strawn March 5 served as a reminder of this reality.

In a statement, the Chicago-based law firm said it had hired seven partners from Jenner & Block, including two practice leaders: Jenner’s private equity chair Mark Harris, who advised Merge Healthcare Inc. in its $1 billion acquisition by IBM, and Alan Roth, chair of Jenner’s investment funds practice.

All seven partners are based in Chicago, but Harris said more could follow.

“We may eventually have lawyers join in other offices,” said Harris, in an interview. “There may be associates or lawyers in other groups. These things go in stages.”

It was less than three years ago when Jenner praised Roth and his colleague Christopher J. Douglass when the pair joined Jenner from a Texas-based firm, Locke Lord, just months after it had acquired Edwards Wildman, the Boston-based firm where Roth and Douglass spent much of their careers.

Harris, for his part, had joined Jenner in 2012, from McDermott Will & Emery, as a key part of the firm’s effort to build its corporate department. He immediately took an expansive title as co-chair of its private equity, hedge fund and investment management practice.

All were part of Jenner’s broader mission to expand the firm’s corporate department, an area Jenner is historically lesser-known for than its litigation and investigations work. Jenner, for instance, was tapped to conduct an investigation into General Motors following recalls related to faulty ignition switches, and also produced the Valukas report, an examination into the demise of Lehman Brothers.

The departures reflect a hiccup in that effort and highlight a recurring issue at large law firms in the hiring and retention of partners: Today, after Jenner has made hires in other areas of its corporate department, such as public company mergers and acquisitions and transactions, Harris and his fellow lawyers found that their practice would fit better at a competitor, he said.

In comments unusually candid for a partner switching firms, Harris acknowledged that the private equity practice did not mesh perfectly with Jenner’s overall practice make-up, but said that he found the work within his group to be personally fulfilling.

“I went to Jenner five years ago with a goal to help build a private equity practice,” said Harris. “It was exciting. They supported us beautifully. We made a number of key lateral hires. And we built that group to be seven partners. We were chugging along and doing well. It was a talented group and a cohesive mix and we got along extremely well.”

What led him to leave the firm is at least partly related to Jenner’s focus on providing legal services to public companies, which meant that the firm had to consider the long-term investment it would make in his own practice, which fell outside of that world, he said.

“I think it’s safe to say that Jenner’s focus was more on the big company side of their practice and that aligns better with their litigation practice,” he said. “It’s not that we didn’t generate litigation work. We certainly did. But not necessarily at the same level or same focus that the litigation side of the firm was anxious to have.”

He added: “About the time that Jenner was wondering whether they wanted to continue to make the significant investments they would have to make to continue to build private equity, other folks were talking to folks in our group about moving to other firms. It became a crossroads for us as to whether Jenner was the right place to build [our practice] or not. Ultimately, we decided Winston’s focus on private equity and the execution they have was really compelling.”

Jenner’s managing partner, Terry Truax, wished the departing lawyers well and acknowledged that, while the firm plans to maintain a private equity practice, its focus on future growth in its corporate department is on public company side clients.

“In the premium or high-end transactional space we are operating in, it remains our view to strategically add talent to our group to meet the demands of our client-centric focus,” said Truax.

Truax rattled off a handful of mergers and acquisitions Jenner had advised on, including its representation of General Dynamics in its $9.6 billion acquisition of CSRA, a public IT company, and Snyder’s Lance’s $4.9 billion pending sale to Campbell’s Soup.

Winston, with 925 lawyers in 16 offices in North America, Asia and Europe, has more than 100 lawyers providing legal services to the private equity industry and 300 in its corporate department. Jenner lists on its website 45 lawyers in its corporate department, and more than 500 lawyers firm wide in five offices: New York, Chicago, Los Angeles, Washington, D.C. and London.

Like Jenner, Winston has also been in the market to expand its corporate department, and has made a number of key additions, including teams of partners from Pillsbury Winthrop Shaw Pittman and Norton Rose Fulbright in New York, as well as partners from a variety of firms in Texas.

Dominick DeChiara, chair of Winston’s transactions department, said that the Jenner group’s “client base and practice is a natural fit for our platform and deeps our M&A, fund formation, and tax capabilities.”

The other Jenner partners joining Winston are tax lawyer Olga Loy, as well as corporate lawyers Jason Osborn, Kate Price and Kyle Gann.

Commenting on the Jenner departures, Kent Zimmermann, a consultant who advises law firms on business issues and has counted Winston & Strawn as a client, said: “You win some, you lose some.”