FULL PRODUCT VERSION :
openjdk version "1.8.0_91"
OpenJDK Runtime Environment (build 1.8.0_91-8u91-b14-3ubuntu1~16.04.1-b14)
OpenJDK 64-Bit Server VM (build 25.91-b14, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Linux francescoUSB 4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

The bug is OS indipendent

A DESCRIPTION OF THE PROBLEM :
In method "java.util.Collections.singletonIterator.forEachRemaining" if consumer throws RuntimeException the single elements is not consumed and may returned multiple times.

Collections.java source code is: (line 4687)
            public void forEachRemaining(Consumer<? super E> action) {
                Objects.requireNonNull(action);
                if (hasNext) {
                    action.accept(e); <--- swap these line
                    hasNext = false; <--- swap these line
                }
            }

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See example code


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.*;

public class Main {

    public static void main(String[] args) {
        Collection<String> elems = Collections.singleton("elem");
        //Collection<String> elems = Arrays.asList("elem"); // this works
        final Iterator<String> elemIterator = elems.iterator();
        try {
            elemIterator.forEachRemaining((e) -> {
                throw new RuntimeException();
            });
        } catch (RuntimeException e) {
            // manage exception
        }
        // elemIterator should be empty now
        System.out.println("Iterator is empty: " + elemIterator.hasNext()); // expected false
        System.out.println("next() method return void: " + elemIterator.next()); // expected NoSuchElementException
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Don't use Collection.singleton* methods