Initialising std::vector from a sequence using std::istringstream

This code:

#include <vector>
#include <string>
#include <iterator>
#include <sstream>
#include <iostream>

int main()
{
    std::vector<std::string>
v(std::istream_iterator<std::string>(std::istringstream("abc bca cab")),
std::istream_iterator<std::string>());
    std::cout << "abc = " << *v.begin() << std::endl;
}

compiles and works. However, I have problems with variations. When I take

std::istringstream("abc bca cab")

out and declare it as a separate variable, to make the code look like this:

//...

int main()
{
    std::istringstream lst("abc bca cab");
    std::vector<std::string> v(std::istream_iterator<std::string>(lst),
std::istream_iterator<std::string>());
    std::cout << "abc = " << *v.begin() << std::endl;
}

the compiler complains like this:

error C2228: left of '.begin' must have class/struct/union

(had I not used the vector variable by commenting out the line where it is
used (with *v.begin()), the code would compile and the compiler would warn

prototyped function not called (was a variable definition intended?)

with reference to the vector initialisation).

To make this variation compile, I declared and initialised the vector
separately:

// ...

int main()
{
    std::istringstream lst("abc bca cab");
    std::vector<std::string> v;
    v.assign(std::istream_iterator<std::string>(lst),
std::istream_iterator<std::string>());
    std::cout << "abc = " << *v.begin() << std::endl;
}

which compiles and works.

This rather puzzles me. Ideally I would want to initialise the vector using
its constructor, yet declare the std::istringstream variable separately. Am I
missing something?

Thank you.

Paul