[Icecast] Client ... has fallen too far behind, removing - but only when listening to a relay, not when listening to fallback

[Nathan Roberts]

I have an icecast server (B) which relays another icecast server (A).
Server B is configured to play a local fallback file when server A is
unavaliable. Both are version 2.3.3

When I listen to server B (the relay), while server A is turned off,
all works fine ie I can listen to the fallback track without problem.
However if I listen to Server B while server A is running then I
quickly get:
INFO source/send_to_listener Client 0 (xx.xx.xx.xx) has fallen too far
behind, removing
where xx.xx.xx.xx is my listening IP address (server A and B being
remote, server B with a good internet connection (Amazon EC2), and
Server A having a more patchy internet connection - hence the reason
for using a relay with fallback.

My internet connection is reliable ADSL, the stream is 64k, and given
the relaibility when on fallback, it doesnt appear credible that the
listening connection has a problem. Any advice on where to start
looking much appreciated. Searches of the mailing list haven't shouwn
anything that appears relivant.

Regards

Nathan