STC: accepts incorrect program with flow typing

@groovy.transform.TypeChecked
class Main {
  public static Bar buz(Foo bux) {
    (((true || bux instanceof Bar)) ?
      bux :
       new Bar())
  }
  public static void main(String[] args) {
    buz(new Foo()).bar()
  }
}

class Foo {
  public void foo() {}
}

class Bar extends Foo {
  public void bar() {}
}

Caught: org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'Foo@2e1792e7' with class 'Foo' to class 'Bar'
org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'Foo@2e1792e7' with class 'Foo' to class 'Bar'
        at Main.buz(Main.groovy:6)
        at Main.main(Main.groovy:9)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)