Distributed builds not always building with dependency changes

We were having problems with our distributed builds not always building when dependencies changed. I traced the issue into:

 org.apache.continuum.builder.distributed.DefaultDistributedBuildService.shouldBuild(Map<String, Object>)

which contains this code fragment:

Date date = ContinuumBuildConstant.getLatestUpdateDate( context );
if ( date != null && oldBuildResult.getLastChangedDate() >= date.getTime() )
{
    log.info( "No changes found, not building (projectId=" + projectId + ")" );
    return false;
}
else if ( date != null && changes.isEmpty() )
{
    // fresh checkout from build agent that's why changes is empty
    log.info( "Changes found in the current project, building (projectId=" + projectId + ")" );
    return true;
}

We seem to be getting caught out by the first test. (There's only one agent building this project btw). I think "oldBuildResult" may be the BuildResult for the current build

I tried commenting out the first piece of logic. This resulted in everything building at every scheduled run because the second test always passes for an existing project with no changes in it.

For now I've commented out ALL of the code above and things seem to be behaving the way I expect.