I have been trying to setup a quotation transformation that will allow me to perform basic Sequence expression evaluation and transform those into NHibernate DetachedCriteria queries. I have pretty much got the property evaluation working but for some reason <@@ Seq.filter @@> doesn't match the SpecificCall pattern:

let (|SequenceFilter|_|) =
function | SpecificCall <@@ Seq.filter @@> (_, [seqty; _],[func;seq]) -> Some(seqty, func, seq)
| _ -> None

Seq.filter has an AST like:

Seq.filter = Lambda (predicate,
Lambda (source,
Call (None,
System.Collections.Generic.IEnumerable`1[System.Object] Filter[Object](Microsoft.FSharp.Core.FSharpFunc`2[System.Object,System.Boolean], System.Collections.Generic.IEnumerable`1[System.Object]),
[predicate, source])))

Has anyone come across this?

EDIT: Looking at a simple filter expression that I am trying to transform it would appeat that the Seq.filter specific call might not match even though the actual call is made:
let entities = Seq.empty
let exp = <@ Seq.filter (fun (a:Entity) -> a.IsActive = true) entites @>
exp = Call (None,
System.Collections.Generic.IEnumerable`1[Entity] Filter[Account](Microsoft.FSharp.Core.FSharpFunc`2[Entity,System.Boolean], System.Collections.Generic.IEnumerable`1[Entity]),
[Lambda (a,
Call (None, Boolean op_Equality[Boolean](Boolean, Boolean),
[PropertyGet (Some (a), Boolean IsActive, []), Value (true)])),
Call (None,
System.Collections.Generic.IEnumerable`1[Entity] enntities [Entity](),
[])])

I have removed some of the plumbing so that the above makes some sense but I would have expected to see a match on the "Filter" call but it appears to get picked up by my last ditch ShapeCombination latter on in the match ... with expression.