diff --git a/examples/example_glfw_opengl3/main.cpp b/examples/example_glfw_opengl3/main.cpp
index d3dcfb37..3ff1cef3 100644
--- a/examples/example_glfw_opengl3/main.cpp
+++ b/examples/example_glfw_opengl3/main.cpp
@@ -98,10 +98,13 @@ int main(int, char**)
     ImGui_ImplOpenGL3_Init(glsl_version);
 
     // Setup Style
-    ImGui::GetStyle().WindowRounding = 0.0f;
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();
 
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.WindowRounding = 0.0f;                                // When viewports are enabled it is preferable to disable WinodwRounding
+    style.Colors[ImGuiCol_WindowBg].w = 1.0f;                   // When viewports are enabled it is preferable to disable WindowBg alpha
+
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple.
diff --git a/examples/example_sdl_opengl3/main.cpp b/examples/example_sdl_opengl3/main.cpp
index 96a91c76..a5a82a7d 100644
--- a/examples/example_sdl_opengl3/main.cpp
+++ b/examples/example_sdl_opengl3/main.cpp
@@ -92,6 +92,10 @@ int main(int, char**)
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();
 
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.WindowRounding = 0.0f;                                // When viewports are enabled it is preferable to disable WinodwRounding
+    style.Colors[ImGuiCol_WindowBg].w = 1.0f;                   // When viewports are enabled it is preferable to disable WindowBg alpha
+
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them. 
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple. 
diff --git a/examples/example_win32_directx11/main.cpp b/examples/example_win32_directx11/main.cpp
index aaf97b46..5fd98c08 100644
--- a/examples/example_win32_directx11/main.cpp
+++ b/examples/example_win32_directx11/main.cpp
@@ -147,10 +147,13 @@ int main(int, char**)
     ImGui_ImplDX11_Init(g_pd3dDevice, g_pd3dDeviceContext);
 
     // Setup Style
-    ImGui::GetStyle().WindowRounding = 0.0f;
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();
 
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.WindowRounding = 0.0f;                                // When viewports are enabled it is preferable to disable WinodwRounding
+    style.Colors[ImGuiCol_WindowBg].w = 1.0f;                   // When viewports are enabled it is preferable to disable WindowBg alpha
+
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them. 
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple. 
diff --git a/imgui.cpp b/imgui.cpp
index 522a0909..ed32c342 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -7427,6 +7427,16 @@ static bool ImGui::UpdateTryMergeWindowIntoHostViewport(ImGuiWindow* window, ImG
     if (GetWindowAlwaysWantOwnViewport(window))
         return false;
 
+    for (int n = 0; n < g.Windows.Size; n++)
+    {
+        ImGuiWindow* window_behind = g.Windows[n];
+        if (window_behind == window)
+            break;
+        if (window_behind->WasActive && window_behind->ViewportOwned && !(window_behind->Flags & ImGuiWindowFlags_ChildWindow))
+            if (window_behind->Viewport->GetRect().Overlaps(window->Rect()))
+                return false;
+    }
+
     // Move to the existing viewport, Move child/hosted windows as well (FIXME-OPT: iterate child)
     ImGuiViewportP* old_viewport = window->Viewport;
     if (window->ViewportOwned)
@@ -7500,7 +7510,10 @@ static void ImGui::UpdateViewports()
             // Clear references to this viewport in windows (window->ViewportId becomes the master data)
             for (int window_n = 0; window_n < g.Windows.Size; window_n++)
                 if (g.Windows[window_n]->Viewport == viewport)
+                {
                     g.Windows[window_n]->Viewport = NULL;
+                    g.Windows[window_n]->ViewportOwned = false;
+                }
             if (viewport == g.MouseLastHoveredViewport) 
                 g.MouseLastHoveredViewport = NULL;
             g.Viewports.erase(g.Viewports.Data + n);
@@ -7687,8 +7700,9 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
     }
 
     // Merge into host viewport
+    bool try_to_merge_into_host_viewport = false;
     if (window->ViewportOwned && g.ActiveId == 0)
-        UpdateTryMergeWindowIntoHostViewport(window, g.Viewports[0]);
+        try_to_merge_into_host_viewport = true;
     window->ViewportOwned = false;
 
     // Appearing popups reset their viewport so they can inherit again
@@ -7719,7 +7733,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         window->Viewport = FindViewportByID(g.NextWindowData.ViewportId);
         window->ViewportId = g.NextWindowData.ViewportId; // Store ID even if Viewport isn't resolved yet.
     }
-    else if ((flags & ImGuiWindowFlags_ChildWindow) && !(flags & ImGuiWindowFlags_ChildMenu))
+    else if ((flags & ImGuiWindowFlags_ChildWindow) || (flags & ImGuiWindowFlags_ChildMenu))
     {
         // Always inherit viewport from parent window
         window->Viewport = window->ParentWindow->Viewport;
@@ -7737,6 +7751,11 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         if (window->Viewport != NULL && window->Viewport->Window == window)
             window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_None);
     }
+    else
+    {
+        if (try_to_merge_into_host_viewport)
+            UpdateTryMergeWindowIntoHostViewport(window, g.Viewports[0]);
+    }
 
     // Fallback to default viewport
     if (window->Viewport == NULL)
@@ -7773,6 +7792,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
             window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoFocusOnAppearing);
         }
     }
+
     // Regular (non-child, non-popup) windows by default are also allowed to protrude
     // Child windows are kept contained within their parent.
     else if (window->ViewportAllowPlatformMonitorExtend < 0 && (flags & ImGuiWindowFlags_ChildWindow) == 0)
diff --git a/imgui.h b/imgui.h
index 4fa1f2a6..6dc4553b 100644
--- a/imgui.h
+++ b/imgui.h
@@ -962,6 +962,7 @@ enum ImGuiConfigFlags_
     ImGuiConfigFlags_DockingNoSplit         = 1 << 7,   // Simplified docking mode: disable window splitting, so docking is limited to merging multiple windows together into tab-bars.
 
     // [BETA] Viewports
+    // When using viewports it is recommended that your default value for ImGuiCol_WindowBg is opaque (Alpha=1.0) so transition to a viewport won't be noticeable.
     ImGuiConfigFlags_ViewportsEnable        = 1 << 10,  // Viewport enable flags (require both ImGuiConfigFlags_PlatformHasViewports + ImGuiConfigFlags_RendererHasViewports set by the respective back-ends)
     ImGuiConfigFlags_ViewportsNoTaskBarIcon = 1 << 11,  // Disable task bars icons for all secondary viewports (will set ImGuiViewportFlags_NoTaskBarIcon on them)
     ImGuiConfigFlags_ViewportsNoMerge       = 1 << 12,  // All floating windows will always create their own viewport and platform window.