LINQ operators that require an IEqualityComparer<T> suck. Do this instead.

DistinctExtensions.cs

using System;
using System.Collections.Generic;

namespace SpaceX.CDL.Core
{
  public class FunctionalEqualityComparer<T> : IEqualityComparer<T>
	{
		private readonly Func<T, T, bool> comparisonFunction;

		public FunctionalEqualityComparer(Func<T, T, bool> comparisonFunction)
		{
			if (comparisonFunction == null)
				throw new ArgumentNullException("comparisonFunction");

			this.comparisonFunction = comparisonFunction;
		}

		public bool Equals(T x, T y)
		{
			return comparisonFunction(x, y);
		}

		public int GetHashCode(T obj)
		{
			return obj.GetHashCode();
		}
	}
}

public static IEnumerable<T> Distinct<T>(this IEnumerable<T> source, Func<T, T, bool> comparisonFunction)
  	{
			if (source == null)
				throw new ArgumentNullException("source");

			if (comparisonFunction == null)
				throw new ArgumentNullException( "comparisonFunction" );

			return source.Distinct( new FunctionalEqualityComparer<T>( comparisonFunction ) );
		}

		public static IEnumerable<T> Distinct<T, U>(this IEnumerable<T> source, Func<T, U> selectorFunction)
		{
			if (source == null)
				throw new ArgumentNullException("source");

			if (selectorFunction == null)
				throw new ArgumentNullException("selectorFunction");

			return
				source.Distinct(
					new FunctionalEqualityComparer<T>(
						(x, y) => EqualityComparer<U>.Default.Equals(selectorFunction(x), selectorFunction(y))));
		}