"Index was outside the bounds of the array" error when executing cached query for single result with distinct results transformer

I have an old codebase (using NHibernate and Castle ActiveRecord) that has been recently upgraded to the 3.2 GA release.

After the upgrade, the following style of queries now fail:

With this stack trace:

NHibernate.Exceptions.GenericADOException: Unable to perform find[SQL: SQL not available] ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
at NHibernate.Type.TypeHelper.Disassemble(Object[] row, ICacheAssembler[] types, Boolean[] nonCacheable, ISessionImplementor session, Object owner) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Type\TypeHelper.cs:line 101
at NHibernate.Cache.StandardQueryCache.Put(QueryKey key, ICacheAssembler[] returnTypes, IList result, Boolean isNaturalKeyLookup, ISessionImplementor session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Cache\StandardQueryCache.cs:line 86
at NHibernate.Loader.Loader.PutResultInQueryCache(ISessionImplementor session, QueryParameters queryParameters, IType[] resultTypes, IQueryCache queryCache, QueryKey key, IList result) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1564
at NHibernate.Loader.Loader.ListUsingQueryCache(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1513
at NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1487
at NHibernate.Loader.Criteria.CriteriaLoader.List(ISessionImplementor session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Loader\Criteria\CriteriaLoader.cs:line 76
at NHibernate.Impl.SessionImpl.List(CriteriaImpl criteria, IList results) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 1948
— End of inner exception stack trace —
at NHibernate.Impl.SessionImpl.List(CriteriaImpl criteria, IList results) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 1959
at NHibernate.Impl.CriteriaImpl.List(IList results) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\CriteriaImpl.cs:line 265
at NHibernate.Impl.CriteriaImpl.List() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\CriteriaImpl.cs:line 256
at NHibernate.Impl.CriteriaImpl.UniqueResult() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\CriteriaImpl.cs:line 428
at NHibernate.Impl.CriteriaImpl.UniqueResult[T]() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\CriteriaImpl.cs:line 282
at Rhino.Commons.RepositoryImplBase`1.FindOne(DetachedCriteria criteria) in

If we remove the distinct results transformer from the query, then the problem goes away.

It's not a big show stopper (In many cases this is old code that incorrectly uses a distinct results transformer when it does not need to) - but I was wondering if this is an expected regression from past behavior, or just a bug?