bootstrapClasspath not working

I have a gradle project that sets a bootstrapClasspath like so:

tasks.withType(JavaCompile) {
  options.bootstrapClasspath = files(project(":haikuRT").tasks["compileJava"].destinationDir, "../lib/nxt/classes.jar")
}

If I do a gradlew build, the project builds without error. However, vscode continues to show compile errors because bootstrapClasspath is not honored. For example, a modification has been made (a method added) to the Thread class however the language server is accessing the Thread class within the JDK.

Environment

• Operating System: Both Windows 10 and OSX 10.12.5
• JDK version: Both 1.8 and 11
• Visual Studio Code version: 1.30.2
• Java extension version: unknown

Steps To Reproduce

1. Clone https://github.com/chuckb/haikuVM
2. ./gradlew build (note that it builds)
3. Observe that the bootstrap subproject has compile errors.

Current Result

Gradle build and vscode show inconsistent results.

Expected Result

vscode should show no compile errors.