IEnumerable reduces when changing it's content?

I have found strange behavior of IEnumerable. When i create a colle开发者_JAVA技巧ction using Linq to XML and than loop the collection and change it's elements, the collection size reduces by 1 on each passing through the loop. Here is what I am talking about:

    var nodesToChange =  from A in root.Descendants()
                         where A.Name.LocalName == "Compile"
                         && A.Attribute("Include").Value.ToLower().Contains(".designer.cs")
                         && A.HasElements && A.Elements().Count() == 1
                         select A;
    foreach (var node in nodesToChange) {
          //after this line the collection is reduced
          node.Attribute("Include").Value = node.Attribute("Include").Value.Replace(".Designer.cs", ".xaml");
    }

But if I add only ToArray<XElement>() to the end of the linq expression, problem is solved.

Can anyone explain me why is this happening? Thanks.

---

The query is evaluated on each loop cycle.

You're changing the Include value so the element is no longer returned from your query, as it doesn't match

A.Attribute("Include").Value.ToLower().Contains(".designer.cs")

By calling ToArray or ToList on your query the loop enumerated a fixed collection, so your manipulation doesn't impact.