插入多行错误，LAST_INSERT_ID()返回0

I am using NHibernate/Fluent NHibernate in an ASP.NET MVC app with a MySQL database. I am working on an operation that reads quite a bit of data (relative to how much is inserted), processes it, and ends up inserting (currently) about 50 records. I have one ISession per request which is created/destroyed in the begin/end request event handlers (exactly like like I am using NHibernate/Fluent NHibernate in an A