[Cppcms-users] app().session().erase() doesn't work or not permitted?

[<ele...@ex...>]

I've just added a simple message to be displayed on website.

ie.
session().set("msg", "User Updated");

And then in my content class I have a get_message() function which gets
called from inside a template.

get_message() does simple -

string msg;

if (app().session().is_set("msg")) {
    msg = app().session().get("msg"); //works
    app().session().erase("msg"); // doesn't work
}

return msg; // always returns text because it never gets erased

Is modifying a session via app().session() not permitted or is it a bug?
Erasing the key from controller works fine.

Another question - why is session_interface::get() not const?

Cheers,
Petr