Here is a build log after two pushes about a minute apart that enqueue two jobs even though the cancel queued job is enabled. Quiet period is 10 minutes.
May 02, 2016 11:36:59 AM FINE org.jenkinsci.plugins.github.pullrequest.webhook.GHPullRequestSubscriber onEvent
Queued check for system-percy (PR #6718) after heavy hook
May 02, 2016 11:36:59 AM FINE org.jenkinsci.plugins.github.pullrequest.webhook.GHPullRequestSubscriber onEvent
Queued check for system-pipeline (PR #6718) after heavy hook
May 02, 2016 11:36:59 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
Running GitHub Pull Request trigger check for May 2, 2016 11:36:59 AM on org/repo
May 02, 2016 11:36:59 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
Running GitHub Pull Request trigger check for May 2, 2016 11:36:59 AM on org/repo
May 02, 2016 11:36:59 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
GitHub rate limit before check: GHRateLimit{remaining=4563, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}
May 02, 2016 11:36:59 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
GitHub rate limit before check: GHRateLimit{remaining=4563, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}
May 02, 2016 11:37:00 AM INFO org.jenkinsci.plugins.github.pullrequest.trigger.check.NotUpdatedPRFilter isUpdated
Pull request #6718 was updated at: Mon May 02 11:37:58 CEST 2016 by mikz
May 02, 2016 11:37:00 AM INFO org.jenkinsci.plugins.github.pullrequest.trigger.check.NotUpdatedPRFilter isUpdated
Pull request #6718 was updated at: Mon May 02 11:37:58 CEST 2016 by mikz
May 02, 2016 11:37:00 AM FINE org.jenkinsci.plugins.github.pullrequest.events.impl.GitHubPRCommitEvent check
New commit. Sha: 6366766cf9cd48f20791d654a66660c2660ec10e => 2bf5ef0679fa3c3573045bbebd4ef28480c2cf6c
May 02, 2016 11:37:01 AM FINE org.jenkinsci.plugins.github.pullrequest.events.impl.GitHubPRLabelNotExistsEvent check
Labels not exist:[percy] not found
May 02, 2016 11:37:01 AM FINEST org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
Causes count for org/repo: 1
May 02, 2016 11:37:01 AM FINEST org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
Causes count for org/repo: 0
May 02, 2016 11:37:02 AM INFO org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
GitHub rate limit after check org/repo: GHRateLimit{remaining=4539, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}, consumed: 24, checked PRs: 1
May 02, 2016 11:37:02 AM INFO org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper info
Finished GitHub Pull Request trigger check for org/repo at May 2, 2016 11:37:02 AM. Duration: 2756ms
May 02, 2016 11:37:02 AM INFO org.jenkinsci.plugins.github.pullrequest.trigger.JobRunnerForCause apply
Jenkins queued the run (Commit changed)
May 02, 2016 11:37:02 AM INFO org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
GitHub rate limit after check org/repo: GHRateLimit{remaining=4535, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}, consumed: 28, checked PRs: 1
May 02, 2016 11:37:02 AM INFO org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper info
Finished GitHub Pull Request trigger check for org/repo at May 2, 2016 11:37:02 AM. Duration: 3230ms
May 02, 2016 11:37:24 AM FINE org.jenkinsci.plugins.github.pullrequest.webhook.GHPullRequestSubscriber onEvent
Queued check for system-percy (PR #6718) after heavy hook
May 02, 2016 11:37:24 AM FINE org.jenkinsci.plugins.github.pullrequest.webhook.GHPullRequestSubscriber onEvent
Queued check for system-pipeline (PR #6718) after heavy hook
May 02, 2016 11:37:24 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
Running GitHub Pull Request trigger check for May 2, 2016 11:37:24 AM on org/repo
May 02, 2016 11:37:24 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
Running GitHub Pull Request trigger check for May 2, 2016 11:37:24 AM on org/repo
May 02, 2016 11:37:25 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
GitHub rate limit before check: GHRateLimit{remaining=4535, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}
May 02, 2016 11:37:25 AM FINE org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper debug
GitHub rate limit before check: GHRateLimit{remaining=4535, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}
May 02, 2016 11:37:25 AM INFO org.jenkinsci.plugins.github.pullrequest.trigger.check.NotUpdatedPRFilter isUpdated
Pull request #6718 was updated at: Mon May 02 11:39:52 CEST 2016 by mikz
May 02, 2016 11:37:25 AM INFO org.jenkinsci.plugins.github.pullrequest.trigger.check.NotUpdatedPRFilter isUpdated
Pull request #6718 was updated at: Mon May 02 11:39:52 CEST 2016 by mikz
May 02, 2016 11:37:26 AM FINE org.jenkinsci.plugins.github.pullrequest.events.impl.GitHubPRCommitEvent check
New commit. Sha: 2bf5ef0679fa3c3573045bbebd4ef28480c2cf6c => 7dfe0a6891bd11147edc47fec18bcf14c746a573
May 02, 2016 11:37:26 AM FINE org.jenkinsci.plugins.github.pullrequest.events.impl.GitHubPRLabelNotExistsEvent check
Labels not exist:[percy] not found
May 02, 2016 11:37:26 AM FINEST org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
Causes count for org/repo: 1
May 02, 2016 11:37:27 AM FINEST org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
Causes count for org/repo: 0
May 02, 2016 11:37:27 AM INFO org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
GitHub rate limit after check org/repo: GHRateLimit{remaining=4517, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}, consumed: 18, checked PRs: 1
May 02, 2016 11:37:27 AM INFO org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper info
Finished GitHub Pull Request trigger check for org/repo at May 2, 2016 11:37:27 AM. Duration: 2617ms
May 02, 2016 11:37:27 AM INFO org.jenkinsci.plugins.github.pullrequest.trigger.JobRunnerForCause apply
Jenkins queued the run (Commit changed)
May 02, 2016 11:37:27 AM INFO org.jenkinsci.plugins.github.pullrequest.GitHubPRTrigger readyToBuildCauses
GitHub rate limit after check org/repo: GHRateLimit{remaining=4513, limit=5000, resetDate=Mon May 02 12:09:55 CEST 2016}, consumed: 22, checked PRs: 1
May 02, 2016 11:37:27 AM INFO org.jenkinsci.plugins.github.pullrequest.utils.LoggingTaskListenerWrapper info
Finished GitHub Pull Request trigger check for org/repo at May 2, 2016 11:37:27 AM. Duration: 3121ms