Looks like the final 1.0 version 1.0-build.3967 is lexigraphically earlier
than the 1.0-beta1-nightly.build.3820 (no idea why).
Please fix that.
It would also help to provide instructions on the
http://jitsi.org/index.php/Main/DebianRepository on how to add the
repository properly (including set up of the GPG keys). BTW, why don't you
use ubuntu PPA to host the files?