Berkshire opened a Lennar position in Q2 last year with 7.05M shares. By the end of June it held 13.1M, having added in three of the four quarters since. About 30% more in the most recent one alone.
Lennar has gone from $133 to $79.70 over the past year. So a good chunk of those adds are underwater, and they kept adding anyway.
That's not how anyone trades a position. It looks more like a price they're happy to own more of at every step down.
For people who know the homebuilders better than I do: what does Berkshire see in Lennar specifically, after selling out of D.R. Horton last year?