Get no RTCP packets in the sender

I've tried to run sender and receiver on two different gentoo systems.
But the sender is always saying: "RTP queue discarded for SSRC"

By commenting out some debugging code in the sender plugin, I think the RTCP receive callback was never fired.
My workaround for now was to don't set the bind-port parameter of the udpsinks and -srcs.
As I see gstreamer sets reuse on the UDP sockets by default, so actually it should work.