json parse u64 broken

[XertroV]

replication:

void Main() {
    auto j = Json::Object();
    j['u64'] = Dev::BaseAddress();
    print(Json::Write(j));
    auto j2 = Json::Parse(Json::Write(j));
    uint64 x = j2['u64'];
    print('' + x);
    print(Text::FormatPointer(x));
}

output:

{"u64":140699673231360}
18446744071562067968
0xFFFFFFFF80000000