RFH: strange message after package upload

[Laszlo 'GCS' Boszormenyi <gcs@lsc.hu>]

Hi,

 My sponsor uploaded sidplay related packages for me. It was like before
with other packages: I get a message that the upload was ok, then that
it was accepted. However for two binary packages I get this snippshet:
-- snip --
(new) libresid-dev_2.1.0-3_i386.deb optional devel
WARNING: Already present in main distribution.
-- snip --

What does it mean, and how can I fix it? The package already contained
this binary package, so it is definiately not new. I have triple checked
that the distribution name is ok: unstable; also it does not happen with
all the binary packages from that source, only with two of them.

Thanks for any hints in advance,
Laszlo/GCS