gbp buildpackage fail: cannot find orig.tar.gz file

Dear Lazyweb,

I had already asked before in Jan but I got same issue.  "gbp buildpackage" command fails...

rm -f ng
make[2]: Leaving directory '/home/henrich/src/pkg-java/nailgun'
rm /home/henrich/src/pkg-java/nailgun/ng-nailgun
rm: cannot remove '/home/henrich/src/pkg-java/nailgun/ng-nailgun': No such file or directory
debian/rules:16: recipe for target 'override_dh_auto_clean' failed
make[1]: [override_dh_auto_clean] Error 1 (ignored)
make[1]: Leaving directory '/home/henrich/src/pkg-java/nailgun'
   dh_clean
gbp:info: Orig tarball 'nailgun_0.9.1.orig.tar.gz' not found at '../tarballs/'
Use of uninitialized value $_[0] in substitution (s///) at /usr/share/perl/5.20/File/Basename.pm line 341.
fileparse(): need a valid pathname at /usr/bin/pristine-tar line 417.
pristine-tar: failed to generate tarball
gbp:error: Couldn't checkout "nailgun_0.9.1.orig.tar.gz": it exited with 255

There IS orig tarball in ../tarballs directory and it works with copying all files to another directory as before...

Yes, and just "cp -arp libspiro /tmp/; cd /tmp/libspiro" and
gbp buildpackage works... (why?)

What causes this and is the best way to solve it?