WPF LifeCyle in an Add-in - wpf

Question

I've created an add-in, which call via Reflection, a WPF Class Library.
Since this is a class library, I had to instanciate manually a new System.Windows.Application().
Then, the class constructor (the one called via reflection) create a window, and Show() (with Dispatcher.Run() to avoid the window to close immediately) or ShowDialog().
Since my application is into an add-in, Application is still alive.
Therefore, I can instanciate this only once.
On the first launch (when Application is instanciated), the Application.Current.Dispatcher is Running.
But on the second launch, I firured out that the Application.Current.Dispatcher was Stopped.
I never call InvokeShutdown() so I don't understand when the Dispatcher is stopped.
When I launch this a second time, Application is already instanciated (it's normal) but Dispatcher stopped.
Any idea ?
Thanks !
Edit : In my Add-in, I've tried 2 ways :
First way :
foreach (Type type in ass2_l.GetTypes())
{
if (type.Name == "Loader")
{
object obj_l = Activator.CreateInstance(type);
BindingFlags bf_l = BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
object[] argList_l = new object[1];
argList_l[0] = "ok";
type.InvokeMember("Load", bf_l, null, obj_l, argList_l);
}
}
When I call directly the dll from the add-in, Application.Current.Dispatcher is in Background State, with name "VSTA_Main".
When I launch a second time, Dispatcher is still in background state.
Second way :
t_m = new Thread(loadDll);
t_m.SetApartmentState(ApartmentState.STA);
t_m.Start();
loadDll actually contain the same code of the "first way" code.
When I launch this part for the first time, the Dispatcher is Running, and all is perfectly normal.
When launched the second time, Dispatcher is stopped.
EDIT 2 :
The problem is in the second way.
When loadDll is finished and then I click again on my add-in button, t_m is stopped and creating another one don't resolve the problem since the Dispatcher ManagedThreadId has the old t_m ManagerThreadId :/
EDIT 3 :
The problem is definately not caused by the Add-in.
If you Just create a program that launch a thread everytime you click on a button.
The thread try to instanciate a DLL WPF Class Library (by reflection), and if you click a second time on this button (calling another thread), as the Dispatcher is still "linked" to the old thread, the Dispatcher is "stopped" (like the old thread)

Answer 1

In ThisAddin.Startup event handler put this code:
private void ThisAddInStartup(object sender, EventArgs e)
{
if (System.Windows.Application.Current == null)
new System.Windows.Application();
System.Windows.Application.Current.ShutdownMode = ShutdownMode.OnExplicitShutdown
}
That should sort it out, it has worked fine for me in the past..

Answer 2

Finally, I solved the problem using an infinite loop to stay the thread in running state, with AutoResetEvent / ManualResetEvent to start/stop the thread...
As the thread never finish (and call a method which load the WPF UI dll when he receive the start event), we never stop the thread (until we stop the Add-in), and the dispatcher is never stopped too.
BTW, thank you for all your answers :)