Index Scan Behaviour When Using ROW_NUMBER() in a View

Here's the scenario...

I have a large table with a PK Clustered index on and INT (ID) column

I create a View on this table which returns the columns from the table and also a derived rank column by using the ROW_NUMBER() OVER PARTITION ordered by the INT(ID) column

When I query the viewed and enter a fixed value for the ID column (example 45) it uses the PK and does an Index Seek which is very fast. However if I put this value in a temp table or normal table and then join this table to the view, the optimizer does an Index Scan. It does not seem to be clever enough to retrieve the value of 45 and the use this value to do a seek

It there a way I can force it to do a seek because for a table with millions of rows the query takes a very very long time :-( Is this normal behaviour and if so why?

You can reproduce this below.Thanks in advance

-- table of data grouped by smallid, with a bigid
CREATE TABLE FOO (
smallid int,
bigid int,
data char(4),
primary key (smallid, bigid)
)
GO

-- populate it with some data
DECLARE @i int
SET @i = 1
WHILE (@i < 1000000) BEGIN
INSERT FOO VALUES (@i, @i%100, 'DATA')
SET @i = @i + 1
END

-- view involves a partitioned row number over the bigid
CREATE VIEW BAR AS
SELECT smallid, bigid, ROW_NUMBER() OVER (PARTITION BY smallid ORDER BY bigid) as _rank
FROM FOO
GO

-- just in case...
update statistics FOO

-- this does a clustered index seek (sweet)
select * from BAR where smallid = 45

-- this doesn't.....
create table #tmp (id int primary key)
insert #tmp values (45)
-- clustered index SCAN!!!!! WHY!?
select * from #tmp inner join BAR on #tmp.id = BAR.smallid
-- or try
select * from BAR inner join #tmp on BAR.smallid = #tmp.id