Jenkins 2.0: $distribution -> how to use with reprepro?

[linuxmail]

hi,
I'm new to Jenkins and got the most things step-by-step working. Now I want to create two Debian packages. One for Wheezy and one for Jessie.
I added in the ..job/jenkins-debian-glue-binaries configuration matrix a second matrix with "distribution" and with "wheezy jessie" as value. Pbuilder creates the correct build env ... one for jessie, one for wheezy, but in the end, the job from Jessie fails, because:

"pool/main/s/sandbox-simulators/sandbox-simulators_2.4+020160520141033.141.gbpb637e1_all.deb" is already registered with different checksums!

What is understandable, because first was the run from wheezy.
The doc is a bit out-dated and short so, I don't fully understand, how I have to configure "jenkins-debian-glue-sources" and "jenkins-debian-glue-binaries".

The next step would, to choose which distribution to build.

Any help would be appreciated :-)