RLC unsoundness at (pseudo?) assignments to `@MustCallUnknown`

The RLC reports no violations on this code, although the resource parameter is clearly dropped without being closed:

import org.checkerframework.checker.mustcall.qual.MustCallUnknown;
import org.checkerframework.checker.mustcall.qual.Owning;

import java.io.Closeable;

public class DropOwning {

  public void f(@Owning Closeable resource) {
    drop(resource);
  }

  private void drop(@Owning @MustCallUnknown Object resource) {
  }

}

The manual suggests that this code should result in a required.method.not.known warning, although that doesn't seem to be the case.

Start with the DropOwning example and the Resource Leak Checker (RLC) behavior described in the issue, then compare it with the manual's resource-leak-generic-unknown section. Reproduce the missing diagnostic and trace how pseudo-assignments to @MustCallUnknown are handled. Done means the example reports the expected required.method.not.known warning.