Just found the bug.

gistfile1.txt

void correct(function<void(char)> f) {
    vector<char> cs {'\x1B','\x25','\x01','\x1B','\x26','\x01'};
    for ( auto c : cs ) f(c);
}

void wrong(Object o) {
    o.print("\x1B\x25\x01\x1B\x26\x01");
}

// wrong is wrong because it prints
// 27 37 1 27 38 1 0
// while correct is correct because it prints
// 27 37 1 27 38 1

// ...sigh...