In resources/tomboynotes/o2/o0globals.h callback urls is hardcoded:
const char O2_CALLBACK_URL[] = "http://127.0.0.1:%1/";
for some reason on my machine tomboynotes was listening only IPv6, took some time to troubleshoot
so if there is already only ipv4 localhost callback URL why not listen on IPv4 only
that way we could avoid wierd issues
QHostAddress::AnyIPv4