When Warren Buffett moves, people watch.

For the most part, Wednesday was a lackluster day for the stock markets, which pulled back slightly after yesterday's record run above 2,100 for the S&P 500 (SNPINDEX:^GSPC). As of 11:15 a.m. EST, the Dow Jones Industrials (DJINDICES:^DJI) were down 41 points, while the S&P 500 had seen a similar percentage drop of about 0.25%. Yet despite the relative quiet in the broader market benchmarks, several stocks saw big moves as a result of the latest SEC filings from Berkshire Hathaway (NYSE:BRK.A) (NYSE:BRK.B): Warren Buffett's most recent switches in his portfolio revealed some mistakes by the Oracle of Omaha, as well as his proposed fixes for those mistakes.

Source: ExxonMobil.

Within the Dow, the biggest impact from the Berkshire moves showed up in ExxonMobil (NYSE:XOM), which fell 1.7%. Oil prices did decline slightly on Wednesday, and fellow oil giant Chevron (NYSE:CVX) also dropped by more than 1%. But Berkshire made the aggressive move of selling off all of its 41 million-share stake in ExxonMobil at some point between last October and December, likely reaping between $3.5 billion and $4 billion in proceeds. Exxon was an unusually short-term holding for Buffett, with Berkshire having just acquired shares in 2013. The about-face was the latest in a series of questionable forays into the energy market for Berkshire, including its ill-timed purchase of ConocoPhillips (NYSE:COP) stock and losses stemming from its purchase of Energy Future Holdings bonds.

On the other side of the ledger, farm equipment maker Deere (NYSE:DE) jumped almost 2%. Berkshire has owned shares of the company for a while, but it publically disclosed its Deere holdings for the first time in its fourth-quarter SEC filing. As of the end of 2014, the stake was worth $1.5 billion, and the stock has avoided the fate of some of its fellow heavy-equipment makers in part because of its agricultural focus. Unlike many of its peers, Deere has relatively little exposure to the energy and materials industries, and that has limited the fallout from plunging oil and metals prices recently.

Source: John Deere.

Finally, not all of Berkshire's new picks celebrated the Buffett news. Twenty-First Century Fox (NASDAQ:FOX) dropped slightly despite Buffett's having reported a 4.7 million-share stake in the multimedia company. Berkshire has emphasized media-industry companies recently, with positions in cable and satellite television providers as well as network and content production companies. Fox shares have been stuck in a holding pattern for much of the past two years, but Buffett clearly hopes that his timing will be good to see a future rise in the importance of media generally and Fox in particular.

Just because Buffett makes a move doesn't mean that you should automatically follow. Yet looking at the impact Berkshire positions can have on the market, it's worth staying up to date on what the Oracle of Omaha is doing with his portfolio.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.