GWTQueryTest.java

import java.util.logging.Logger;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.query.client.Function;
import com.google.gwt.query.client.Promise;
import com.google.gwt.query.client.plugins.deferred.PromiseFunction;
import com.google.gwt.user.client.Timer;

public class GWTQueryTest implements EntryPoint {
	private final Logger log = Logger.getLogger("GWTQueryTest");

	@Override
	public void onModuleLoad() {
		executionOrder();
		errorHandling();
	}

	/**
	 * The error seems to disappear
	 */
	private void errorHandling() {
		final Promise promise = timeOut(100);
		promise.then(new Function() {
			public void f() {
				throw new Error("I want to fail");
			}
		}, new Function() {
			public void f() {
				log.info("Not here? Nope");
			}
		}).fail(new Function() {
			public void f() {
				log.info("How about here? Nope");
			}
		});
	}

	/**
	 * This is a duplicate of the example in http://stackoverflow.com/a/23744774
	 */
	private void executionOrder() {
		log.info("This");
		final Promise promise = timeOut(1000);
		promise.then(new Function() {
			public void f() {
				log.info("expected from an async api");
			}
		});
		log.info("is");
		Timer timer = new Timer() {

			@Override
			public void run() {
				log.info("He");
				promise.then(new Function() {
					public void f() {
						log.info("BAD THINGS");
					}
				});
				log.info("comes");
			}

		};
		timer.schedule(2000);
	}

	/**
	 * Simple function that resolves a promise after a set delay
	 * 
	 * @param delay
	 * @return {@link Promise}
	 */
	private Promise timeOut(final int delay) {
		Promise promise = new PromiseFunction() {

			@Override
			public void f(final Deferred dfd) {
				Timer t = new Timer() {
					@Override
					public void run() {
						dfd.resolve();
					}
				};
				t.schedule(delay);
			}
		};
		return promise;
	}

}

Testing if GWTQuery inherited the incorrect implementation of promises in JQuery seen in this stackoverflow question.

Answer: it seems to, the error vanishes and the execution order is incorrect.