It took me around 1 hour to find how it fails only(it doesn't fail when run individually)
If you run NH1556 and DetachedQueryFixture one after the other, for example, it fails. The Sql produced for the query
new DetachedQuery("from Foo f where f.Name=:pn and f.Description=:pd");
is
exec sp_executesql N'select foo0_.Id as Id4_, foo0_.Name as Name4_, foo0_.Description as Descript3_4_, foo0_.IntValue as IntValue4_ from Foos foo0_ where (foo0_.Name=@p0 )and(foo0_.Description=@p0 )',N'@p0 nvarchar(2),@p1 nvarchar(2)',@p0=N'N2',@p1=N'D2'
which is faulty, however, when run individually
exec sp_executesql N'select foo0_.Id as Id0_, foo0_.Name as Name0_, foo0_.Description as Descript3_0_, foo0_.IntValue as IntValue0_ from Foos foo0_ where (foo0_.Name=@p0 )and(foo0_.Description=@p1 )',N'@p0 nvarchar(2),@p1 nvarchar(2)',@p0=N'N2',@p1=N'D2'
which is correct.
I have to study Operating Systems now, will try to look deeper later today, hopefuly.