Post-Join Filter expression doesn't work

[funlambda]

I'm unable to get filters applied after doing an outer join to work. Here's my query in C#:

Query.Db("test")
     .Table<Util.Stored<Scrape.ScrapeResult>>("ScrapeResults")
     .OuterJoin(Query.Db("test").Table<Scrape.IgnoredScrapeResult>("IgnoredScrapeResults"), 
                (sr, isr) => sr.ID == isr.IgnoredID)
     .Filter(y => y.Item2 == null)
     .Map(x => x.Item1)

I'm getting this exception message:

Failed to perform client-side evaluation of expression tree node 'y.Item2'; this is caused by refering to a server-side variable in an expression tree that isn't convertible to ReQL logic

Full stack trace: exception.txt