Hi Ubiratan,
as an extension to Iain's answer I like to add some points.
To some extend the mistake is even that you are trying to build on a
stable machine. The final package goes to unstable and it *has* *to*
build with the original libqextserialport-dev package from unstable.
Everything else will be broken. If you in addition want to provide a
backport to stable that's something else and should be dealt with in a
separate step. As said previously building a package in unstable is
usually done with pbuilder (or rather the flavour of cowbuilder). Could
you please confirm that you have setup a cowbuilder chroot using
sudo cowbuilder --create
? This is in so far essential since we need to be sure that we are
talking about the same thing and not about some local modifications at
your side which we can not reproduce.
Before filing a bug report please
1. Commit your work to a Vcs of your choice (either Git or SVN)
as described in Debian Med team policy