Why can eosiocpp not do normal operations on std::vector<std::string>?

Question

I have two types:

struct typeA {
    std::vector<std::string> vec;
}

struct typeB {
    std::vector<std::string> vec;
}

but I can't seem to get the 2 vecs to mix as eosiocpp seems to be treating them as std::vector of unsigned char or something whenever I try to iterate or perform insert() on them. Literally:

typeA objA;
typeB objB;


for (auto s : objB.vec) {
    objA.vec.push_back(s); //<-- throws errors
}

//or

objB.vec.insert(objB.vec.end(), objA.vec.begin(), objA.vec.end()); //<-- throws errors

the errors being

candidate function not viable: no known conversion from 'unsigned char' to
  'const value_type' (aka 'const std::__1::basic_string<char>') for 1st argument

and

 note: candidate function not viable: no known conversion from 'const_iterator'
  (aka '__wrap_iter<const unsigned char *>') to 'size_type' (aka 'unsigned int') for 2nd argument
iterator insert(const_iterator __position, size_type __n, const_reference __x);
         ^
 note: candidate template ignored: disabled by 'enable_if' [with _InputIterator =
  std::__1::__wrap_iter<const unsigned char *>]
         __is_input_iterator  <_InputIterator>::value &&

(which seems to be it's own set of problems as well).

Kind of pulling my hair out here.