boost::program_options: option recognizes following option as an argument when no argument is provided

I have a program that takes a few options and I want to recognize when no argument is provided.

This is what happen when I call my program without one option arg

program -lib

cout: the required argument for option '-lib' is missing

That's ok, but when I call my program with additional options, e.g

program -lib -out number

The variable assigned to lib gets the value "-out", although -out was declared as an option. I expect to get the same warning as in the first example.

I can solve this problem by adding a custom notifier to all the options, code below:

void validate_string(const std::string& r)
{
    if (*r.begin() == '-') { 
            throw Something
    }
}

...

("lib", po::value<std::string>(&lib)->notifier(validate_string), "Library")

There's any way of doing this with a build-in mechanism of boost::program_options? I don't like my current solution, the options declaration look messy and is hard to read. Besides -out is not getting assigned.

BTW: I use allow_long_disguise, so single - is allowed for long options