Use a quit bool in B_ABOUT_REQUESTED to indicate that the about window has quit instead of using kAboutWindowClosed message. This prevents message signature clashes.

headers/private/shared/AboutWindow.h

@@ -11,8 +11,6 @@
 #include <View.h>
 
 
-const int32 kAboutWindowClosed = 'abwc';
-
 class AboutView;
 class BPoint;
 class BHandler;

src/apps/activitymonitor/ActivityView.cpp

@@ -1112,6 +1112,13 @@ ActivityView::MessageReceived(BMessage* message)
 
 	switch (message->what) {
 		case B_ABOUT_REQUESTED:
+		{
+			bool quit = false;
+			if (message->FindBool("quit", &quit) == B_OK && quit) {
+				fAboutWindow = NULL;
+				break;
+			}
+
 			if (fAboutWindow == NULL) {
 				fAboutWindow = new BAboutWindow(this, kAppName, kSignature);
 				fAboutWindow->AddCopyright(2008, "Haiku, Inc.");
@@ -1120,10 +1127,7 @@ ActivityView::MessageReceived(BMessage* message)
 				fAboutWindow->Activate();
 
 			break;
-
-		case kAboutWindowClosed:
-			fAboutWindow = NULL;
-			break;
+		}
 
 		case kMsgUpdateResolution:
 		{

src/apps/deskcalc/CalcView.cpp

@@ -270,6 +270,13 @@ CalcView::MessageReceived(BMessage* message)
 
 			// (replicant) about box requested
 			case B_ABOUT_REQUESTED:
+			{
+				bool quit = false;
+				if (message->FindBool("quit", &quit) == B_OK && quit) {
+					fAboutWindow = NULL;
+					break;
+				}
+
 				if (fAboutWindow == NULL) {
 					// create the about window
 					const char* extraCopyrights[] = {
@@ -285,10 +292,7 @@ CalcView::MessageReceived(BMessage* message)
 					fAboutWindow->Activate();
 
 				break;
-
-			case kAboutWindowClosed:
-				fAboutWindow = NULL;
-				break;
+			}
 
 			case MSG_UNFLASH_KEY:
 			{

src/apps/processcontroller/ProcessController.cpp

@@ -426,6 +426,13 @@ ProcessController::MessageReceived(BMessage *message)
 		}
 
 		case B_ABOUT_REQUESTED:
+		{
+			bool quit = false;
+			if (message->FindBool("quit", &quit) == B_OK && quit) {
+				fAboutWindow = NULL;
+				break;
+			}
+
 			if (fAboutWindow == NULL) {
 				const char* extraCopyrights[] = {
 					"1997-2001 Georges-Edouard Berenger",
@@ -446,10 +453,7 @@ ProcessController::MessageReceived(BMessage *message)
 				fAboutWindow->Activate();
 
 			break;
-
-		case kAboutWindowClosed:
-			fAboutWindow = NULL;
-			break;
+		}
 
 		default:
 			BView::MessageReceived(message);

src/kits/shared/AboutWindow.cpp

@@ -248,8 +248,12 @@ BAboutWindow::QuitRequested()
 	if (fCaller != NULL) {
 		status_t status;
 		BMessenger messenger(fCaller, NULL, &status);
-		if (status == B_OK && messenger.IsValid())
-			messenger.SendMessage(new BMessage(kAboutWindowClosed));
+		if (status == B_OK && messenger.IsValid()) {
+			BMessage* message = new BMessage(B_ABOUT_REQUESTED);
+			message->AddBool("quit", true);
+			messenger.SendMessage(message);
+			delete message;
+		}
 	}
 
 	return true;

src/preferences/locale/LocalePreflet.cpp

@@ -73,6 +73,13 @@ LocalePreflet::MessageReceived(BMessage* message)
 			break;
 
 		case B_ABOUT_REQUESTED:
+		{
+			bool quit = false;
+			if (message->FindBool("quit", &quit) == B_OK && quit) {
+				fAboutWindow = NULL;
+				break;
+			}
+
 			if (fAboutWindow == NULL) {
 				const char* authors[] = {
 					"Axel Dörfler",
@@ -89,10 +96,7 @@ LocalePreflet::MessageReceived(BMessage* message)
 				fAboutWindow->Activate();
 
 			break;
-
-		case kAboutWindowClosed:
-			fAboutWindow = NULL;
-			break;
+		}
 
 		default:
 			BApplication::MessageReceived(message);