Removing an item from collection which is iterated in foreach loop

See more:

C#

LINQ

Check the code below:

class Program
    {
        class TestClass
        {
            public int MyProperty { get; set; }

            public int MyProperty1 { get; set; }
        }

        static void Main(string[] args)
        {
            Collection<testclass> testCollection = new Collection<testclass>();
            testCollection.Add(new TestClass());
            testCollection.Add(new TestClass());
            
            var test = (from str in testCollection
                        select new {p1 = str.MyProperty, p2 = str.MyProperty1});

            foreach (var item in test)
            {
                testCollection.Remove(testCollection.Where(x => x.MyProperty1 == item.p2).First());
            }
        }
    }</testclass></testclass>

It throws InvalidOperationException when the loop is executed for the second time. Now just change the LINQ expression as below:

var test = (from str in testCollection
            select new {p1 = str.MyProperty, p2 = str.MyProperty1}).ToList();

It works! My assumption is that ToList method creates a deep copy before converting the return types and hence it works. It looks like my assumption is correct since when I debug, I can see that the variable test is unchanged when I remove the item from the collection. Can someone confirm? Or I am totally on a wrong track?