Short seller Douglas Kass has won his relatively short-term bet against Warren Buffett. Given Buffett's decades-long track record as the world's greatest investor, he doesn't lose very often.

In March, Kass listed 11 Reasons to Short Berkshire on TheStreet.com. (Going 'short' is, in effect, a bet that a particular stock will go down in price, not up.)

Kass, who is president of Seabreeze Partners Management, generated some headlines in May when he discussed his short position in an interview with Barron's. Hecited Buffett's "recent investment-style drift" that had left him "immersed ... in several large and thus far unprofitable derivative transactions." Kass also talked about weakness in Berkshire's insurance businesses, Buffett's exposure to financials, and the weak housing market. Plus, he pointed out, Buffett won't be running Berkshire forever and "investors are going to dump the shares if Buffett is no longer at the helm."

In an appearance on CNBC a few days later, Kass told Larry Kudlow:

"Yogi Berra once said, 'Even Napoleon had his Watergate.' (Laughs.) And in the case of Warren Buffett, his Watergate is an investment-style drift which is really a no-no in the money management business... You have to stick to your knitting... Look, I worship at the knee of Warren Buffett and all he's accomplished over the years. But the reality is in the last decade he's underperformed dramatically and he's drifted in terms of strategy."

Then in June, Kass wrote that he had added to his short position, citing "bombs in Buffett's book." He pointed to "poor short-term and long-term charts " for four of Berkshire's biggest stock holdings: Coca-Cola , Wells Fargo , Kraft , and American Express . (Only Wells Fargo has gained ground since then.)

Kass's endorsement this week of Buffett's high-profile call to buy U.S. stocks prompted us to ask him if he's still short Berkshire.

In an email reply, Kass told us he first shorted Berkshire in February of this year, when the shares were trading around $145,000, "as there was no 'margin of safety' against my calculation of intrinsic value."

And he revealed, "I am no longer short Berkshire Hathaway - I covered my short position around $115,000/share in August as it fulfilled my price objective on the downside."