cannot change value of QString and std::string variables in locals view

I have the following code in my test program:

    QString qs = u"foo"_qs;
    std::string s = "foo";
    int i = 156;
    qDebug() << qs << s.c_str() << i;

with a breakpoint at the last line.

Once the breakpoint is hit, I change the values of i, s and qs in the locals view.
For the int it works fine.

For the string types, the view immediately reverts to the original value.