Lambda implementing override-equivalent methods doesn't have return type checked against both

import org.checkerframework.checker.nullness.qual.Nullable;

interface Supplier1<T> {
  T get();
}

interface Supplier2<T> {
  T get();
}

interface BothSuppliers<T> extends Supplier1<T>, Supplier2<@Nullable T> {}

class Foo {
  public static void main(String[] args) {
    BothSuppliers<String> s = () -> null;
    ((Supplier1<String>) s).get().length();
  }
}

$ checker/bin/javac -processor org.checkerframework.checker.nullness.NullnessChecker Foo.java && java Foo
Exception in thread "main" java.lang.NullPointerException
  at Foo.main(Foo.java:16)

The lambda's return type is being checked against Supplier1.get() but not Supplier2.get(): If I switch the location of the @Nullable from Supplier1<T>, Supplier2<@Nullable T> to Supplier1<@Nullable T>, Supplier2<T>, then the Checker Framework detects the problem. And if I switch from a lambda to a class, the Checker Framework also detects the problem.

Source file and -version -verbose -AprintAllQualifiers output attached.