diff --git a/src/servers/app/ServerWindow.cpp b/src/servers/app/ServerWindow.cpp
index 63f846cf68..0f47d68acf 100644
--- a/src/servers/app/ServerWindow.cpp
+++ b/src/servers/app/ServerWindow.cpp
@@ -293,12 +293,10 @@ ServerWindow::Show()
 	// NOTE: if you do something else, other than sending a port message, PLEASE lock
 	STRACE(("ServerWindow %s: Show\n", Title()));
 
-	if (fQuitting || !fWindowLayer->IsHidden())
+	if (fQuitting || !fWindowLayer->IsHidden() || fWindowLayer->IsOffscreenWindow())
 		return;
 
-	// TODO: that check is just there for offscreen-windows - this should be made better
-	if (fWindowLayer->GetRootLayer() != NULL)
-		fDesktop->ShowWindow(fWindowLayer);
+	fDesktop->ShowWindow(fWindowLayer);
 
 	if (fDirectWindowData != NULL)
 		HandleDirectConnection(B_DIRECT_START | B_BUFFER_RESET);
@@ -312,15 +310,13 @@ ServerWindow::Hide()
 	// NOTE: if you do something else, other than sending a port message, PLEASE lock
 	STRACE(("ServerWindow %s: Hide\n", Title()));
 
-	if (fWindowLayer->IsHidden())
+	if (fWindowLayer->IsHidden() || fWindowLayer->IsOffscreenWindow())
 		return;
 
 	if (fDirectWindowData != NULL)
 		HandleDirectConnection(B_DIRECT_STOP);
 
-	// TODO: that check is just there for offscreen-windows - this should be made better
-	if (fWindowLayer->GetRootLayer() != NULL)
-		fDesktop->HideWindow(fWindowLayer);
+	fDesktop->HideWindow(fWindowLayer);
 }
 
 
@@ -1323,19 +1319,18 @@ ServerWindow::_DispatchMessage(int32 code, BPrivate::LinkReceiver &link)
 		{
 			STRACE(("ServerWindow %s: Message AS_SET_LOOK\n", Title()));
 
+			status_t status = B_ERROR;
 			int32 look;
-			if (link.Read<int32>(&look) != B_OK) {
-				fLink.StartMessage(B_ERROR);
-				fLink.Flush();
-				break;
+			if (link.Read<int32>(&look) == B_OK) {
+				// test if look is valid
+				status = WindowLayer::IsValidLook((window_look)look)
+					? B_OK : B_BAD_VALUE;
 			}
 
-			// TODO: filter out invalid looks
-
-			if (!fWindowLayer->IsOffscreenWindow())
+			if (status == B_OK && !fWindowLayer->IsOffscreenWindow())
 				fDesktop->SetWindowLook(fWindowLayer, (window_look)look);
 
-			fLink.StartMessage(B_OK);
+			fLink.StartMessage(status);
 			fLink.Flush();
 			break;
 		}
@@ -1346,18 +1341,9 @@ ServerWindow::_DispatchMessage(int32 code, BPrivate::LinkReceiver &link)
 			status_t status = B_ERROR;
 			int32 feel;
 			if (link.Read<int32>(&feel) == B_OK) {
-				// test if "feel" is valid
-				status = (feel == B_NORMAL_WINDOW_FEEL
-						|| feel == B_MODAL_SUBSET_WINDOW_FEEL
-						|| feel == B_MODAL_APP_WINDOW_FEEL
-						|| feel == B_MODAL_ALL_WINDOW_FEEL
-						|| feel == B_FLOATING_SUBSET_WINDOW_FEEL
-						|| feel == B_FLOATING_APP_WINDOW_FEEL
-						|| feel == B_FLOATING_ALL_WINDOW_FEEL
-						|| feel == kDesktopWindowFeel
-						|| feel == kMenuWindowFeel
-						|| feel == kWindowScreenFeel)
-					? B_BAD_VALUE : B_OK;
+				// test if feel is valid
+				status = WindowLayer::IsValidFeel((window_feel)feel)
+					? B_OK : B_BAD_VALUE;
 			}
 
 			if (status == B_OK && !fWindowLayer->IsOffscreenWindow())
@@ -1365,25 +1351,26 @@ ServerWindow::_DispatchMessage(int32 code, BPrivate::LinkReceiver &link)
 
 			fLink.StartMessage(status);
 			fLink.Flush();
+			break;
 		}
 		case AS_SET_FLAGS:
 		{
 			STRACE(("ServerWindow %s: Message AS_SET_LOOK\n", Title()));
 
+			status_t status = B_ERROR;
 			uint32 flags;
-			if (link.Read<uint32>(&flags) != B_OK) {
-				fLink.StartMessage(B_ERROR);
-				fLink.Flush();
-				break;
+			if (link.Read<uint32>(&flags) == B_OK) {
+				// test if flags are valid
+				status = (flags & ~WindowLayer::ValidWindowFlags()) != 0
+					? B_OK : B_BAD_VALUE;
 			}
 
-			// TODO: filter out invalid flags
-
-			if (!fWindowLayer->IsOffscreenWindow())
+			if (status == B_OK && !fWindowLayer->IsOffscreenWindow())
 				fDesktop->SetWindowFlags(fWindowLayer, flags);
 
-			fLink.StartMessage(B_OK);
+			fLink.StartMessage(status);
 			fLink.Flush();
+			break;
 		}
 #if 0
 		case AS_SET_ALIGNMENT:
diff --git a/src/servers/app/WindowLayer.cpp b/src/servers/app/WindowLayer.cpp
index cd0ca255c5..7efee6e7d0 100644
--- a/src/servers/app/WindowLayer.cpp
+++ b/src/servers/app/WindowLayer.cpp
@@ -89,6 +89,13 @@ WindowLayer::WindowLayer(const BRect &frame,
 	  fMinHeight(1.0),
 	  fMaxHeight(32768.0)
 {
+	// make sure our arguments are valid 
+	if (!IsValidLook(fLook))
+		fLook = B_TITLED_WINDOW_LOOK;
+	if (!IsValidFeel(fFeel))
+		fFeel = B_NORMAL_WINDOW_FEEL;
+	fFlags &= ValidWindowFlags();
+
 	// unlike BViews, windows start off as hidden
 	fHidden = true;
 	fWindow = window;
@@ -853,3 +860,53 @@ WindowLayer::SetTopLayer(Layer* layer)
 	}
 }
 
+
+/*static*/
+bool
+WindowLayer::IsValidLook(window_look look)
+{
+	return look == B_TITLED_WINDOW_LOOK
+		|| look == B_DOCUMENT_WINDOW_LOOK
+		|| look == B_MODAL_WINDOW_LOOK
+		|| look == B_FLOATING_WINDOW_LOOK
+		|| look == B_BORDERED_WINDOW_LOOK
+		|| look == B_NO_BORDER_WINDOW_LOOK
+		|| look == kDesktopWindowLook
+		|| look == kLeftTitledWindowLook;
+}
+
+
+/*static*/
+bool
+WindowLayer::IsValidFeel(window_feel feel)
+{
+	return feel == B_NORMAL_WINDOW_FEEL
+		|| feel == B_MODAL_SUBSET_WINDOW_FEEL
+		|| feel == B_MODAL_APP_WINDOW_FEEL
+		|| feel == B_MODAL_ALL_WINDOW_FEEL
+		|| feel == B_FLOATING_SUBSET_WINDOW_FEEL
+		|| feel == B_FLOATING_APP_WINDOW_FEEL
+		|| feel == B_FLOATING_ALL_WINDOW_FEEL
+		|| feel == kDesktopWindowFeel
+		|| feel == kMenuWindowFeel
+		|| feel == kWindowScreenFeel;
+}
+
+
+/*static*/
+uint32
+WindowLayer::ValidWindowFlags()
+{
+	return B_NOT_MOVABLE | B_NOT_CLOSABLE | B_NOT_ZOOMABLE
+		| B_NOT_MINIMIZABLE | B_NOT_RESIZABLE
+		| B_NOT_H_RESIZABLE | B_NOT_V_RESIZABLE
+		| B_AVOID_FRONT | B_AVOID_FOCUS
+		| B_WILL_ACCEPT_FIRST_CLICK | B_OUTLINE_RESIZE
+		| B_NO_WORKSPACE_ACTIVATION
+		| B_NOT_ANCHORED_ON_ACTIVATE
+		| B_ASYNCHRONOUS_CONTROLS
+		| B_QUIT_ON_WINDOW_CLOSE
+		| kWorkspacesWindowFlag
+		| kWindowScreenFlag;
+}
+
diff --git a/src/servers/app/WindowLayer.h b/src/servers/app/WindowLayer.h
index 5a65b43023..fbc06792fd 100644
--- a/src/servers/app/WindowLayer.h
+++ b/src/servers/app/WindowLayer.h
@@ -119,6 +119,10 @@ class WindowLayer : public Layer {
 	inline	Layer*				TopLayer() const
 									{ return fTopLayer; }
 
+	static bool					IsValidLook(window_look look);
+	static bool					IsValidFeel(window_feel feel);
+	static uint32				ValidWindowFlags();
+
  protected:
 	virtual void				_AllRedraw(const BRegion& invalid);