C++11 regex::icase inconsistent behavior

Question

Coming from perl-like regular expressions, I expected the below code to match regex'es in all 8 cases. But it doesn't. What am I missing?

#include <iostream>
#include <regex>
#include <string>

using namespace std;

void check(const string& s, regex re) {
    cout << s << " : " << (regex_match(s, re) ? "Match" : "Nope") << endl;
}

int main() {
    regex re1 = regex("[A-F]+", regex::icase);
    check("aaa", re1);
    check("AAA", re1);
    check("fff", re1);
    check("FFF", re1);
    regex re2 = regex("[a-f]+", regex::icase);
    check("aaa", re2);
    check("AAA", re2);
    check("fff", re2);
    check("FFF", re2);
}

Running with gcc 5.2:

$ g++ -std=c++11 test.cc -o test && ./test
aaa : Match
AAA : Match
fff : Nope
FFF : Match
aaa : Match
AAA : Match
fff : Match
FFF : Nope

Answer 1

For future users, this was confirmed to be a bug, and it (and similar issues) are solved as of 8.1 according to this thread.

I suspect that the original author had a hand in bringing attention to this, but I figured maybe we could get this closed.