I'm trying to use a GroupBy with a custom generic class : this is failing with a translation error. Why is my query failing and what can I do to fix it?

Working query

var query = Query.All<MyEntity>().GroupBy(i => new { Key1 = i.Text, Key2 = i.Text2 });

Query failing with a translation error : Internal error: Unable to remap KeyExpression

var query = Query.All<MyEntity>().GroupBy(i => new  GroupKey<string,string> { Key1 = i.Text, Key2 = i.Text2 });

  public class GroupKey<T1, T2>
  {
    public T1 Key1 { get; set; }
    public T2 Key2 { get; set; }
  }

EDIT:

version 4.4.2.8034

Xtensive.Orm.QueryTranslationException occurred
  Message=Unable to translate 'Query.All().Where( => True).GroupBy( => new GroupKey<String>() {
  Key1 = .Supplier
})' expression. See inner exception for details.
  Source=Xtensive.Orm
  StackTrace:
       at Xtensive.Orm.Linq.QueryProvider.Translate[TResult](Expression expression)
       at Xtensive.Orm.Linq.QueryProvider.Execute[TResult](Expression expression)
       at Xtensive.Orm.Linq.Queryable`1.GetEnumerator()
       at Xtensive.Orm.Linq.Queryable`1.System.Collections.IEnumerable.GetEnumerator()
  InnerException: System.InvalidOperationException
       Message=Internal error: Unable to remap KeyExpression.
       Source=Xtensive.Orm
       StackTrace:
            at Xtensive.Orm.Linq.Expressions.KeyExpression.Remap(Int32[] map, Dictionary`2 processedExpressions)
            at Xtensive.Orm.Linq.Expressions.EntityExpression.Remap(Int32[] map, Dictionary`2 processedExpressions)
            at Xtensive.Orm.Linq.Expressions.FieldExpression.Remap(Int32[] map, Dictionary`2 processedExpressions)
            at Xtensive.Orm.Linq.ConstructorExpression.<>c__DisplayClass1a.<Remap>b__15(IMappedExpression mapped)
            at Xtensive.Orm.Linq.Expressions.Visitors.GenericExpressionVisitor`1.VisitGenericExpression(T generic)
            at Xtensive.Orm.Linq.Expressions.Visitors.GenericExpressionVisitor`1.VisitUnknown(Expression e)
            at Xtensive.Linq.ExpressionVisitor`1.Visit(Expression e)
            at Xtensive.Orm.Linq.Expressions.Visitors.GenericExpressionVisitor`1.Process(Expression target, Func`2 genericProcessor)
            at Xtensive.Orm.Linq.ConstructorExpression.<>c__DisplayClass1a.<Remap>b__17(KeyValuePair`2 kvp)
            at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
            at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
            at Xtensive.Orm.Linq.ConstructorExpression.Remap(Int32[] map, Dictionary`2 processedExpressions)
            at Xtensive.Orm.Linq.Expressions.ItemProjectorExpression.<>c__DisplayClass4.<Remap>b__3(IMappedExpression mapped)
            at Xtensive.Orm.Linq.Expressions.Visitors.GenericExpressionVisitor`1.VisitGenericExpression(T generic)
            at Xtensive.Orm.Linq.Expressions.Visitors.GenericExpressionVisitor`1.VisitUnknown(Expression e)
            at Xtensive.Linq.ExpressionVisitor`1.Visit(Expression e)
            at Xtensive.Orm.Linq.Expressions.Visitors.GenericExpressionVisitor`1.Process(Expression target, Func`2 genericProcessor)
            at Xtensive.Orm.Linq.Expressions.ItemProjectorExpression.Remap(RecordQuery dataSource, Int32[] columnMap)
            at Xtensive.Orm.Linq.Translator.VisitGroupBy(Type returnType, Expression source, LambdaExpression keySelector, LambdaExpression elementSelector, LambdaExpression resultSelector)
            at Xtensive.Orm.Linq.Translator.VisitQueryableMethod(MethodCallExpression mc, QueryableMethodKind methodKind)
            at Xtensive.Linq.QueryableVisitor.VisitMethodCall(MethodCallExpression mc)
            at Xtensive.Orm.Linq.Translator.VisitMethodCall(MethodCallExpression mc)
            at Xtensive.Linq.ExpressionVisitor`1.Visit(Expression e)
            at Xtensive.Orm.Linq.Translator.Visit(Expression e)
            at Xtensive.Orm.Linq.Translator.Translate[TResult]()
            at Xtensive.Orm.Linq.QueryProvider.Translate[TResult](Expression expression)
       InnerException: