Composition should end if we have selection.

Source/core/paint/InlineTextBoxPainter.cpp

Index: Source/core/paint/InlineTextBoxPainter.cpp
diff --git a/Source/core/paint/InlineTextBoxPainter.cpp b/Source/core/paint/InlineTextBoxPainter.cpp
index f288e7cba5170d2934f8954a49f5a5a84ec9cd07..be34f8270263f8b9779b6de8662ebfb62972318b 100644
--- a/Source/core/paint/InlineTextBoxPainter.cpp
+++ b/Source/core/paint/InlineTextBoxPainter.cpp
@@ -77,7 +77,7 @@ void InlineTextBoxPainter::paint(const PaintInfo& paintInfo, const LayoutPoint&
     }
 
     // Determine whether or not we have composition underlines to draw.
-    bool containsComposition = m_inlineTextBox.layoutObject().node() && m_inlineTextBox.layoutObject().frame()->inputMethodController().compositionNode() == m_inlineTextBox.layoutObject().node();
+    bool containsComposition = !haveSelection && m_inlineTextBox.layoutObject().node() && m_inlineTextBox.layoutObject().frame()->inputMethodController().compositionNode() == m_inlineTextBox.layoutObject().node();
     bool useCustomUnderlines = containsComposition && m_inlineTextBox.layoutObject().frame()->inputMethodController().compositionUsesCustomUnderlines();
 
     // The text clip phase already has a DrawingRecorder. Text clips are initiated only in BoxPainter::paintLayerExtended, which is already
@@ -155,7 +155,7 @@ void InlineTextBoxPainter::paint(const PaintInfo& paintInfo, const LayoutPoint&
 
         paintDocumentMarkers(context, boxOrigin, styleToUse, font, true);
 
-        if (haveSelection && !useCustomUnderlines) {
+        if (haveSelection) {
             if (combinedText)
                 paintSelection<InlineTextBoxPainter::PaintOptions::CombinedText>(context, boxRect, styleToUse, font, selectionStyle.fillColor, combinedText);
             else