I find that for example, using PMD Parser when the recordIssues has a quality gate set and there is a failure case for the quality gate, the build is not 'halted' and the next pipeline step executes, though the build is marked failed. if 'unstable: true' is set, the build is marked unstable and halts, but not when 'unstable: false'

My understanding and expectation here is that if recordIssues determines the quality gate FAILS, the build should be marked failed AND no following Pipeline steps should execute.    

According to docs here

https://github.com/jenkinsci/warnings-ng-plugin/blob/master/doc/Documentation.md#quality-gate-configuration

the build should fail.

Example I have here in declarative pipeline:

stage("PMD Check") {
 steps

{ sh "./gradlew --no-daemon pmd" }

post {
 always

{ recordIssues referenceJobName: 'mobileheros_multibranch/develop', enabledForFailure: true, qualityGates: [[threshold: 685, type: 'TOTAL_HIGH', unstable: false], [threshold: 1, type: 'NEW', unstable: false]], tools: [pmdParser(pattern: 'Rewards/build/reports/pmd/*.xml')] }

}
 }

stage("TEST ME") {
 steps

{ echo "WHY DID THIS EXECUTE???" }

}

log from Jenkins:
BUILD SUCCESSFUL in 2m 23s
1 actionable task: 1 executedPost stage[Pipeline] stepusing credential ***
[PMD] Searching for all files in '/Users/Shared/Jenkins/Home/jobs/POC Pipeline/branches/develop/workspace' that match the pattern 'Rewards/build/reports/pmd/*.xml'
[PMD] -> found 1 file
[PMD] Successfully parsed file /Users/Shared/Jenkins/Home/jobs/POC Pipeline/branches/develop/workspace/Rewards/build/reports/pmd/pmd.xml
[PMD] -> found 14604 issues (skipped 2001 duplicates)
> git rev-parse HEAD^{commit} # timeout=10
[PMD] Post processing issues on 'Master' with source code encoding 'UTF-8'
[PMD] Resolving absolute file names for all issues in workspace '/Users/Shared/Jenkins/Home/jobs/POC Pipeline/branches/develop/workspace'
[PMD] -> 0 resolved, 0 unresolved, 925 already resolved
[PMD] Copying affected files to Jenkins' build folder '/Users/Shared/Jenkins/Home/jobs/POC Pipeline/branches/develop/builds/2/files-with-issues'
[PMD] -> 925 copied, 0 not in workspace, 0 not-found, 0 with I/O error
[PMD] Resolving module names from module definitions (build.xml, pom.xml, or Manifest.mf files)
[PMD] -> resolved module names for 14604 issues
[PMD] Resolving package names (or namespaces) by parsing the affected files
[PMD] -> all affected files already have a valid package name
[PMD] No filter has been set, publishing all 14604 issues
[PMD] Creating fingerprints for all affected code blocks to track issues over different builds
[PMD] -> created fingerprints for 14604 issues
[PMD] Invoking Git blamer to create author and commit information for all affected files
[PMD] GIT_COMMIT env = 'HEAD'
[PMD] Git working tree = '/Users/Shared/Jenkins/Home/jobs/POC Pipeline/branches/develop/workspace'
[PMD] Git commit ID = '434b4d1f9b677d54fadd57550ac3af7d4d3a1325'
[PMD] Job workspace = '/Users/Shared/Jenkins/Home/jobs/POC Pipeline/branches/develop/workspace'
[PMD] Created blame requests for 925 files - invoking Git blame on agent for each of the requests
[PMD] -> blamed authors of issues in 925 files
[PMD] Attaching ResultAction with ID 'pmd' to run 'POC Pipeline/develop #2'.
[PMD] Using reference build 'mobileheros_multibranch/develop #204' to compute new, fixed, and outstanding issues
[PMD] Issues delta (vs. reference build): outstanding: 14600, new: 4, fixed: 6
[PMD] Evaluating quality gates
[PMD] -> PASSED - Total number of warnings (severity high): 451 - Quality QualityGate: 685
[PMD] -> FAILED - Number of new issues (any severity): 4 - Quality QualityGate: 1
[PMD] -> Some quality gates have been missed: overall result is FAILED
[PMD] Health report is disabled - skipping
[PMD] Created analysis result for 14604 issues (found 4 new issues, fixed 6 issues)[Pipeline] }[Pipeline] // stage[Pipeline] stage[Pipeline]

[Pipeline] // stage[Pipeline] stage[Pipeline] { (Declarative: Post Actions)[Pipeline] echoFINALLY DONE WITH RESULT=FAILURE[Pipeline] sh