ReSharperInterpolationBug.cs

using System;

namespace ReSharperBugs
{
    internal class Program
    {
        private static void Main()
        {
            var sideEffectOccurred = false;

            try
            {
                //
                // 1. Run and note the result (sideEffectOccurred = true).
                // 2. Apply "Use string interpolation" quick fix.
                // 3. Run again, note that the result changes (sideEffectOccurred = false).
                //
                Console.WriteLine(
                    string.Format(
                        "{0:BadFormat}: " +
                        "{1}",
                        Guid.Empty,
                        sideEffectOccurred = true));
            }
            catch {}
            finally
            {
                Console.WriteLine("sideEffectOccurred: {0}", sideEffectOccurred);
                Console.ReadLine();
            }
        }
    }
}