When rebuilding parts of a matrix job (using the matrix reloaded plugin), the build will then trigger all downstream jobs. In our case, the downstream jobs are also matrix jobs and we would like that in this case, the downstream jobs are also "reloaded", i.e. only the parts that were rebuilt in the upstream job should be built there as well.

To reproduce, I've used a setup that somewhat resembles what we have:

• 2 matrix jobs, jobA and jobB
• jobA has jobB as its downstream job
• each job consists of a 3x3 matrix with the axis labelled "compiler" and "os" respectively
• the compiler axis has values FORTE, GCC, MSC
• the os axis has values solaris, linux, windows
• the build step is just a echo "hello world"

We're using the Parameterized Build plugin, http://wiki.jenkins-ci.org/display/JENKINS/Parameterized+Trigger+Plugin, to trigger downstream builds but this can also be reproduced with the standard "Build other projects" option.

The two screenshots show the matrix and which parts are supposed to be rebuild. The second screenshot shows that jobB, when triggered by rebuilding only parts of the jobA matrix, is actually building all 9 combinations, not just the 2 of the upstream job.

P.S. I mentioned this problem at the Jenkins User Conference in Paris, in case you remember