Selector.startBuild() returns non-build objects from stdout and resulting selector sometimes doesn't contain any build object

[mkaspar]

I'm trying to modify buildconfig in OpenShift and then run build from it (using --from-dir) wait for the build to finish and return resulting logs. However when i start the build from the buildconfig, the startBuild() returns 3 objects instead of just build each corresponding to one line of oc start-build --from-dir=xxx output and narrrowing the result to Build object type returns 0 objects in parallel builds even though the build is running and finishes.
The relevant code (k8sObjects contains IS and BC definitions):

openshift.withCluster() {
   openshift.withProject(BUILD_NAMESPACE) {
      builders['imageX'] = {
         ...
        def applySelector = openshift.apply(k8sObjects);
        def bcSelector = applySelector.narrow('BuildConfig');
        def buildSelector = bcSelector.startBuild("--from-dir=.")
        echo "Static selector names: ${buildSelector.names()}, ${buildSelector.narrow('Build').names()}"
        timeout(10) {
           buildSelector.narrow('Build').untilEach(1) {
              return it.object().status.phase == 'Complete' || it.object().status.phase == 'Failed';
           }
         }
      }
      parallel builders
   }
}

Output:

Static selector names: [Uploading directory "." as binary input for the build ..., ., Uploading finished, build/ceos-cmd-setup-35], [build/ceos-cmd-setup-35]
Static selector names: [Uploading directory "." as binary input for the build ..., /ceos-cmd-app-repository-100, Uploading finished], []
...
 ERROR: Selector is static and empty; watch would never terminate.

oc get build
ceos-cmd-app-repository-100        Docker   Binary@97c7b0d   Complete                          6 minutes ago    3m59s
ceos-cmd-setup-35                  Docker   Binary@97c7b0d   Complete                          6 minutes ago    3m56s

There was a build that succeded with a bit different output (mind the build name versus Uploading finished parts of the startBuild selector):

 Static selector names: [Uploading directory "." as binary input for the build ..., ., Uploading finished, build/ceos-cmd-setup-34], [build/ceos-cmd-setup-34]
Static selector names: [Uploading directory "." as binary input for the build ..., ., Uploading finished, build/ceos-cmd-app-repository-99], [build/ceos-cmd-app-repository-99]

So it looks like the selector selecting the build seems to work based on start-build output ordering.
Would be nice if the startBuild() selector returned only the build irrelevant of the other ouptut lines.