C# already computes the right insertion text when we make the item. No need to recompute it.

src/Features/CSharp/Portable/Completion/CompletionProviders/SymbolCompletionProvider.cs

@@ -35,7 +35,7 @@ protected override bool IsInstrinsic(ISymbol s)
         protected override string GetInsertionText(
             CompletionItem item, ISymbol symbol, SyntaxContext context, char ch)
         {
-            return GetInsertionText(symbol, context);
+            return SymbolCompletionItem.GetInsertionText(item);
         }
 
         public static string GetInsertionText(ISymbol symbol, SyntaxContext context)