Originally reported under #2244, incorrect query is generated for

var selectedProducts = new[] { productDefinition1 };
var query = session.Query<Material>()
	.Where(x => selectedProducts.Contains(x.ProductDefinition) && selectedProducts.Select(y => y.MaterialDefinition).Contains(x.MaterialDefinition));

.Select(y => y.MaterialDefinition) is ignored and IDs of product definitions are inserted into the list of material definitions, i.e. SQL contains query to the effect of ... where MaterialDefinitionId in (ProductDefinitionId1, ProductDefinitionId2, ...).

Original standalone unit test: https://github.com/v-kabanov/Nh526QueryBug/blob/68498cf1f440db8694474f1b55a5efa31be2ae41/MyTest.cs#L207

New unit test integrated in a fork of NH repo added in commit v-kabanov@133b26d

It runs and fails but needs some further development.