Hello Marcos,
I don't use sbuild but pbuilder and the package built OK on my
machine.
Anyway, as buildd's use sbuild (AFAIK), i think that this issue
needs to be investigated. I will try to put some time tomorrow
Please note that the problem itself is with the autopkgtest of the package, build is ok, you will only spot it if you enable such tests. That is: the package is not FTBFSing, but the autopkgtests are failing.
I mentioned sbuild because given the nature of the problem, I can see it not happening on build environments that aren't well isolated, thus sbuild is one way of ensuring the problem will be reproducible, I'm not familiar with pbuilder but I suppose you would be able to see the same problem if running autopkgtest there.
I would recommend taking a look at the sbuild page and considering using it as your build tool, you can very easily integrate with piuparts, lintian, autopkgtest, apt-cacher-ng and ccache, I find it the best solution to build a package.
Regards,