diff --git a/OpenUtau.Core/Ustx/UExpression.cs b/OpenUtau.Core/Ustx/UExpression.cs
index 8ccf660a1..cf9e294ba 100644
--- a/OpenUtau.Core/Ustx/UExpression.cs
+++ b/OpenUtau.Core/Ustx/UExpression.cs
@@ -116,5 +116,7 @@ public UExpression Clone() {
                 value = value,
             };
         }
+
+        public override string ToString() => $"{abbr.ToUpper()}: {value}";
     }
 }
diff --git a/OpenUtau.Core/Ustx/UProject.cs b/OpenUtau.Core/Ustx/UProject.cs
index 8597b8e19..c8b57d9b2 100644
--- a/OpenUtau.Core/Ustx/UProject.cs
+++ b/OpenUtau.Core/Ustx/UProject.cs
@@ -90,23 +90,27 @@ public void MargeExpression(string oldAbbr, string newAbbr) {
                 parts.Where(p => p is UVoicePart)
                     .OfType<UVoicePart>()
                     .ForEach(p => p.notes.ForEach(n => ConvertNoteExp(n, tracks[p.trackNo])));
-            } else if (voiceParts != null &&voiceParts.Count > 0) {
+            } else if (voiceParts != null && voiceParts.Count > 0) {
                 voiceParts.ForEach(p => p.notes.ForEach(n => ConvertNoteExp(n, tracks[p.trackNo])));
             }
             expressions.Remove(oldAbbr);
 
             void ConvertNoteExp(UNote note, UTrack track) {
                 if (note.phonemeExpressions.Any(e => e.abbr == oldAbbr)) {
-                    note.phonemeExpressions.ForEach(oldExp => {
+                    var toRemove = new List<UExpression>();
+                    note.phonemeExpressions.Where(e => e.abbr == oldAbbr).ForEach(oldExp => {
                         if (!note.phonemeExpressions.Any(newExp => newExp.abbr == newAbbr && newExp.index == oldExp.index)) {
+                            // When there is only old exp, convert it to new exp
                             oldExp.abbr = newAbbr;
                             if (track.TryGetExpDescriptor(this, newAbbr, out var descriptor)) {
                                 oldExp.descriptor = descriptor;
                             }
                         } else {
-                            note.phonemeExpressions.Remove(oldExp);
+                            // When both old and new exp exist, remove the old one
+                            toRemove.Add(oldExp);
                         }
                     });
+                    toRemove.ForEach(exp => note.phonemeExpressions.Remove(exp));
                 }
             }
         }