Internals: Windows hidden with HiddenFramesRegular (but NOT HiddenFramesForResize) preserve their SizeContents, so restoring a auto-resize window after it's been hidden by tabs won't reset its size for a frame. Arguable. Let's see how it goes. (Followup to b48e295bddbf965d7382ec5578ed05d2fe601114)

imgui.cpp

@@ -4242,6 +4242,9 @@ static ImVec2 CalcSizeAfterConstraint(ImGuiWindow* window, ImVec2 new_size)
 
 static ImVec2 CalcSizeContents(ImGuiWindow* window)
 {
+    if (window->Hidden && window->HiddenFramesForResize == 0 && window->HiddenFramesRegular > 0)
+        return window->SizeContents;
+
     ImVec2 sz;
     sz.x = (float)(int)((window->SizeContentsExplicit.x != 0.0f) ? window->SizeContentsExplicit.x : (window->DC.CursorMaxPos.x - window->Pos.x + window->Scroll.x));
     sz.y = (float)(int)((window->SizeContentsExplicit.y != 0.0f) ? window->SizeContentsExplicit.y : (window->DC.CursorMaxPos.y - window->Pos.y + window->Scroll.y));