if the buildresult is set to trigger with a schedule of every minute
(* * * * ) and you have a long runnign upstream job, the job with a trigger will trigger when the upstream job **starts building*

This appears to be due to a Null POinter Exception as the trigger gets the status of the LastBuild - but the lastBuild may be currently building and return a null status.

see private boolean isMatchingExpectedResults(String jobName, CheckedResult[] expectedResults, XTriggerLog log) in src/main/java/org/jenkinsci/plugins/buildresulttrigger/BuildResultTrigger.java

Polling started on Jul 25, 2013 2:47:53 PM
Polling for the job cms-at_master-LEVEL-1
Looking nodes where the poll can be run.
Looking for a candidate node to run the poll.
Trying to find an eligible node with the assigned project label RH53_ATC.

Polling remotely on cabci-cf-rh53-x64-atc01
Checking changes for job CMS/cms-subsystem/cms-subsystem/commit.
There are no new builds for the job CMS/cms-subsystem/cms-subsystem/commit.
Checking changes for job CMS/vcm/vcm-app/commit.
There is at least one new build for the job CMS/vcm/vcm-app/commit. Checking expected job build results.
Checking SUCCESS
[ERROR] - Polling error...

See also the output from the script console

AbstractProject jobObj = Hudson.getInstance().getItemByFullName("CMS/vcm/vcm-app/commit/", AbstractProject.class);
Run jobObjLastBuild = jobObj.getLastBuild();
Result jobObjectLastResult = jobObjLastBuild.getResult();

println("run: " + jobObjLastBuild.number);
println("status: " + jobObjLastBuild.result);
println("isBuilding: " + jobObjLastBuild.building);

run: 1089
status: null
isBuilding: true

The polling error then causes a build to be triggered which will trigger the build prematurely and when the build has finished the build will not be triggered.