<p>Assume you are doing something like the following</p>

<pre><code>List&lt;string&gt; myitems = new List&lt;string&gt;
{
    "Item 1",
    "Item 2",
    "Item 3"
};

ComboBox box = new ComboBox();
box.DataSource = myitems;

ComboBox box2 = new ComboBox();
box2.DataSource = myitems
</code></pre>

<p>So now we have 2 combo boxes bound to that array, and everything works fine. But when you change the value of one combo box, it changes BOTH combo boxes to the one you just selected.</p>

<p>Now, I know that Arrays are always passed by reference (learned that when i learned C :D), but why on earth would the combo boxes change together? I don't believe the combo box control is modifying the collection at all. </p>

<p>As a workaround, don't this would achieve the functionality that is expected/desired</p>

<pre><code>ComboBox box = new ComboBox();
box.DataSource = myitems.ToArray();
</code></pre>

This has to do with how data bindings are set up in the dotnet framework, especially the
```
BindingContext
```
. On a high level it means that if you haven't specified otherwise each form and all the controls of the form share the same
```
BindingContext
```
. When you are setting the
```
DataSource
```
property the
```
ComboBox
```
will use the
```
BindingContext
```
to get a
```
ConcurrenyMangager
```
that wraps the list. The
```
ConcurrenyManager
```
keeps track of such things as the current selected position in the list.
When you set the
```
DataSource
```
of the second
```
ComboBox
```
it will use the same
```
BindingContext
```
(the forms) which will yield a reference to the same
```
ConcurrencyManager
```
as above used to set up the data bindings.
To get a more detailed explanation see
BindingContext
.