One Megabyte Memcpy

A profiler shows a 1 MB memcpy at line B, which the author believed was a move.

class Buffer {
public:
    explicit Buffer(std::size_t n) : n_(n), data_(new char[n]) {}
    ~Buffer() { delete[] data_; }
    Buffer(const Buffer& o) : n_(o.n_), data_(new char[o.n_]) {
        std::memcpy(data_, o.data_, n_);
    }
private:
    std::size_t n_;
    char* data_;
};

std::vector<Buffer> v;
v.reserve(4);
Buffer b(1 << 20);
v.push_back(std::move(b));   // B

Why does line B copy?