CPU is hogged when using std::vector of std::unique_ptrs

I have a Qt Widgets application that uses C++11. I have a very simple main.cpp that creates and uses a std::vector<std::unique_ptr<Obj>>. When I open main.cpp for edit, Qt Creator begins to consume one whole CPU. Every time I make a single-character edit, the CPU usage goes up by one CPU. Trying to quit leads it to hang, seemingly forever.

#include <vector>
#include <memory>

struct Obj
{
    int fun() { return 1; }
};

int main(int argc, char *argv[])
{
    std::vector<std::unique_ptr<Obj>> vec;
    vec.front()->fun();
    return 0;
}

The problem seems to only happen when I have the line vec.front()->fun(), and specifically only when I'm using the arrow operator on a unique_ptr that's in the vector.