Index: Application.cs
===================================================================
--- Application.cs	(revision 61538)
+++ Application.cs	(working copy)
@@ -83,13 +83,15 @@
 					int		loops;
 					MWFThread	thread;
 
-					e = threads.Values.GetEnumerator();
-					loops = 0;
+					lock (threads) {
+						e = threads.Values.GetEnumerator();
+						loops = 0;
 
-					while (e.MoveNext()) {
-						thread = (MWFThread)e.Current;
-						if (thread != null && thread.messageloop_started) {
-							loops++;
+						while (e.MoveNext()) {
+							thread = (MWFThread)e.Current;
+							if (thread != null && thread.messageloop_started) {
+								loops++;
+							}
 						}
 					}
 
@@ -132,7 +134,9 @@
 						Application.ApplicationExit(null, EventArgs.Empty);
 					}
 				}
-				threads[thread_id] = null;
+				lock (threads) {
+					threads.Remove (thread_id);
+				}
 			}
 			#endregion	// Methods
 		}
@@ -493,7 +497,7 @@
 
 				// Handle exit, Form might have received WM_CLOSE and set 'closing' in response
 				if ((context.MainForm != null) && (context.MainForm.closing || (Modal && !context.MainForm.Visible))) {
-					if (!Modal) {
+					if (!Modal && MWFThread.LoopCount == 1) {
 						XplatUI.PostQuitMessage(0);
 					} else {
 						break;