diff --git a/imgui.cpp b/imgui.cpp
index 4280e1b9..94d97dc2 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -1971,7 +1971,7 @@ static void SetCurrentWindow(ImGuiWindow* window)
     ImGuiContext& g = *GImGui;
     g.CurrentWindow = window;
     if (window)
-        g.FontSize = window->CalcFontSize();
+        g.FontSize = g.DrawListSharedData.FontSize = window->CalcFontSize();
 }
 
 static void SetNavID(ImGuiID id, int nav_layer)
@@ -3254,8 +3254,9 @@ void ImGui::NewFrame()
     g.OsImePosRequest = ImVec2(1.0f, 1.0f); // OS Input Method Editor showing on top-left of our window by default
 
     // If mouse was first clicked outside of ImGui bounds we also cancel out hovering.
-    // FIXME: For patterns of drag and drop between "application" and "imgui" we may need to rework/remove this test (first committed 311c0ca9 on 2015/02)
-    if (!mouse_avail_to_imgui)
+    // FIXME: For patterns of drag and drop across OS windows, we may need to rework/remove this test (first committed 311c0ca9 on 2015/02)
+    bool mouse_dragging_extern_payload = g.DragDropActive && (g.DragDropSourceFlags & ImGuiDragDropFlags_SourceExtern) != 0;
+    if (!mouse_avail_to_imgui && !mouse_dragging_extern_payload)
         g.HoveredWindow = g.HoveredRootWindow = NULL;
 
     // Scale & Scrolling
@@ -6817,7 +6818,7 @@ void ImGui::SetWindowFontScale(float scale)
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = GetCurrentWindow();
     window->FontWindowScale = scale;
-    g.FontSize = window->CalcFontSize();
+    g.FontSize = g.DrawListSharedData.FontSize = window->CalcFontSize();
 }
 
 // User generally sees positions in window coordinates. Internally we store CursorPos in absolute screen coordinates because it is more convenient.
@@ -12035,9 +12036,11 @@ static float OffsetNormToPixels(const ImGuiColumnsSet* columns, float offset_nor
 
 static float PixelsToOffsetNorm(const ImGuiColumnsSet* columns, float offset)
 {
-    return (offset - columns->MinX) / (columns->MaxX - columns->MinX);
+    return offset / (columns->MaxX - columns->MinX);
 }
 
+static inline float GetColumnsRectHalfWidth() { return 4.0f; }
+
 static float GetDraggedColumnOffset(ImGuiColumnsSet* columns, int column_index)
 {
     // Active (dragged) column always follow mouse. The reason we need this is that dragging a column to the right edge of an auto-resizing
@@ -12047,7 +12050,7 @@ static float GetDraggedColumnOffset(ImGuiColumnsSet* columns, int column_index)
     IM_ASSERT(column_index > 0); // We cannot drag column 0. If you get this assert you may have a conflict between the ID of your columns and another widgets.
     IM_ASSERT(g.ActiveId == columns->ID + ImGuiID(column_index));
 
-    float x = g.IO.MousePos.x - g.ActiveIdClickOffset.x - window->Pos.x;
+    float x = g.IO.MousePos.x - g.ActiveIdClickOffset.x + GetColumnsRectHalfWidth() - window->Pos.x;
     x = ImMax(x, ImGui::GetColumnOffset(column_index - 1) + g.Style.ColumnsMinSpacing);
     if ((columns->Flags & ImGuiColumnsFlags_NoPreserveWidths))
         x = ImMin(x, ImGui::GetColumnOffset(column_index + 1) - g.Style.ColumnsMinSpacing);
@@ -12120,7 +12123,7 @@ void ImGui::SetColumnOffset(int column_index, float offset)
 
     if (!(columns->Flags & ImGuiColumnsFlags_NoForceWithinWindow))
         offset = ImMin(offset, columns->MaxX - g.Style.ColumnsMinSpacing * (columns->Count - column_index));
-    columns->Columns[column_index].OffsetNorm = PixelsToOffsetNorm(columns, offset);
+    columns->Columns[column_index].OffsetNorm = PixelsToOffsetNorm(columns, offset - columns->MinX);
 
     if (preserve_width)
         SetColumnOffset(column_index + 1, offset + ImMax(g.Style.ColumnsMinSpacing, width));
@@ -12184,7 +12187,7 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiColumnsFlag
     // Set state for first column
     const float content_region_width = (window->SizeContentsExplicit.x != 0.0f) ? (window->SizeContentsExplicit.x) : (window->Size.x -window->ScrollbarSizes.x);
     columns->MinX = window->DC.IndentX - g.Style.ItemSpacing.x; // Lock our horizontal range
-    //column->ColumnsMaxX = content_region_width - window->Scroll.x -((window->Flags & ImGuiWindowFlags_NoScrollbar) ? 0 : g.Style.ScrollbarSize);// - window->WindowPadding().x;
+    //column->MaxX = content_region_width - window->Scroll.x - ((window->Flags & ImGuiWindowFlags_NoScrollbar) ? 0 : g.Style.ScrollbarSize);// - window->WindowPadding().x;
     columns->MaxX = content_region_width - window->Scroll.x;
     columns->StartPosY = window->DC.CursorPos.y;
     columns->StartMaxPosX = window->DC.CursorMaxPos.x;
@@ -12212,7 +12215,7 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiColumnsFlag
         ImGuiColumnData* column = &columns->Columns[n];
         float t = column->OffsetNorm;
         if (!(columns->Flags & ImGuiColumnsFlags_NoForceWithinWindow))
-            t = ImMin(t, PixelsToOffsetNorm(columns, columns->MaxX - g.Style.ColumnsMinSpacing * (columns->Count - n)));
+            t = ImMin(t, PixelsToOffsetNorm(columns, (columns->MaxX - columns->MinX) - g.Style.ColumnsMinSpacing * (columns->Count - n)));
         column->OffsetNorm = t;
 
         if (n == columns_count)
@@ -12257,7 +12260,7 @@ void ImGui::EndColumns()
         {
             float x = window->Pos.x + GetColumnOffset(n);
             const ImGuiID column_id = columns->ID + ImGuiID(n);
-            const float column_hw = 4.0f; // Half-width for interaction
+            const float column_hw = GetColumnsRectHalfWidth(); // Half-width for interaction
             const ImRect column_rect(ImVec2(x - column_hw, y1), ImVec2(x + column_hw, y2));
             KeepAliveID(column_id);
             if (IsClippedEx(column_rect, column_id, false))
@@ -12269,8 +12272,6 @@ void ImGui::EndColumns()
                 ButtonBehavior(column_rect, column_id, &hovered, &held);
                 if (hovered || held)
                     g.MouseCursor = ImGuiMouseCursor_ResizeEW;
-                if (held && g.ActiveIdIsJustActivated)
-                    g.ActiveIdClickOffset.x -= column_hw; // Store from center of column line (we used a 8 wide rect for columns clicking). This is used by GetDraggedColumnOffset().
                 if (held && !(columns->Columns[n].Flags & ImGuiColumnsFlags_NoResize))
                     dragging_column = n;
             }
diff --git a/imgui_demo.cpp b/imgui_demo.cpp
index 392a11bd..e064e278 100644
--- a/imgui_demo.cpp
+++ b/imgui_demo.cpp
@@ -1741,7 +1741,10 @@ void ImGui::ShowTestWindow(bool* p_open)
 
         if (ImGui::TreeNode("Keyboard, Mouse & Navigation State"))
         {
-            ImGui::Text("Mouse pos: (%g, %g)", io.MousePos.x, io.MousePos.y);
+            if (ImGui::IsMousePosValid())
+                ImGui::Text("Mouse pos: (%g, %g)", io.MousePos.x, io.MousePos.y);
+            else
+                ImGui::Text("Mouse pos: <INVALID>");
             ImGui::Text("Mouse down:");     for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++) if (io.MouseDownDuration[i] >= 0.0f)   { ImGui::SameLine(); ImGui::Text("b%d (%.02f secs)", i, io.MouseDownDuration[i]); }
             ImGui::Text("Mouse clicked:");  for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++) if (ImGui::IsMouseClicked(i))          { ImGui::SameLine(); ImGui::Text("b%d", i); }
             ImGui::Text("Mouse dbl-clicked:"); for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++) if (ImGui::IsMouseDoubleClicked(i)) { ImGui::SameLine(); ImGui::Text("b%d", i); }