Dynamically loading different assemblies that are copies of each other

I've written a pluggable application that loads plugins as assemblies. Each plugin reads an XML configuration file which basically has different string settings.

Everything works fine with different plugins, but I'm experiencing strange behavior when I copy and paste an existing plugin assembly dll (but change it's XML configuration).

Plugin A    |- PluginA.dll
            |- PluginA.xml

Plugin B    |- PluginB.dll
            |- PluginB.xml

The original assembly (A) and copied assembly (B) are loaded, but it seems that that the application has loaded the exact same plugin (B) twice.

I know this because the plugin interface has a property called 'ApplicationName' and the value is read from the XML file in the appropriate plugin. The XML file is being read for each plugin correctly, and the property values are supposed to be 'A' and 'B', respectively.

foreach (var pluginFile in LoadedPluginFiles) // 2 different plugin filenames
    {
       LogMessage("Loading plugin: " + pluginFile); // correct filename in loop
       ObjectHandle oHandle = Activator.CreateInstanceFrom(pluginFile, "MailboxMonitorPlugin.MailboxMonitorPlugin");
       MailboxMonitorPlugin.IMailboxMonitorPlugin pluginInfo = oHandle.Unwrap() as IMailboxMonitorPlugin;
       pluginInfo.Initialize(MailLink.Service.Properties.Settings.Default.PluginsPath);
       LogMessage("Plugin Application Name: " + pluginInfo.ApplicationName.ToString()); // Same application name (B) even though different file loaded in the loop.

After I load the plugins, I write the property names out to the log, and the plugin has it's property read twice.

Is there a low-level operation happening here that I don't understand? Perhaps a pointer to the same assembly because they're exactly the same objects?