Docking: Fixed size constraints not working on single window holding on a dock id (still doesn't work on docked windows).

docs/CHANGELOG.txt

@@ -231,6 +231,8 @@ Other Changes:
 
 Docking+Viewports Branch:
 
+- Docking: Fixed a CTRL+TAB crash when aiming at an empty docked window. (#4792)
+- Docking: Fixed size constraints not working on single window holding on a dock id (still doesn't work on docked windows).
 - Viewports, IO: Added io.AddMouseViewportEvent() function to queue hovered viewport change (when known by backend).
 - Viewports: Relaxed specs for backend supporting ImGuiBackendFlags_HasMouseHoveredViewport: it is now _optional_
   for the backend to have to ignore viewports with the _NoInputs flag when call io.AddMouseViewportEvent(). It is
@@ -240,7 +242,6 @@ Docking+Viewports Branch:
   io.AddMouseViewportEvent() function, then Dear ImGui will revert to its flawed heuristic to find the viewport under.
   By lowering those specs, we allow the SDL and more backend to support this, only relying on the heuristic in a few
   drag and drop situations rather that relying on it everywhere.
-- Docking: Fixed a CTRL+TAB crash when aiming at an empty docked window. (#4792)
 - Viewports: Fixed a CTRL+TAB crash with viewports enabled when the window list needs to appears in
   its own viewport (regression from 1.86). (#4023, #787)
 - Viewports: Fixed active InputText() from preventing viewports to merge. (#4212)

imgui.cpp

@@ -6383,7 +6383,8 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
                 IM_ASSERT(window->DockNode != NULL);
 
             // Docking currently override constraints
-            g.NextWindowData.Flags &= ~ImGuiNextWindowDataFlags_HasSizeConstraint;
+            if (window->DockIsActive)
+                g.NextWindowData.Flags &= ~ImGuiNextWindowDataFlags_HasSizeConstraint;
 
             // Amend the Appearing flag
             if (window->DockTabIsVisible && !dock_tab_was_visible && dock_node_was_visible && !window->Appearing && !window_was_appearing)