Computed Column Issue

Hi,

I'm having a problem with a computed field in a table. I have a stored procedure that inserts a row into a table and returns the id and the computed value.
The computed colmn is returned as a decimal (29,6) but for some reason the value is returned with no decimals (confirmed by the Profiler).
The value is calculated and displayed in the database properly with decimals. Also, Is Persisted is OFF.

Below is the stored procedure, computed column foruma (both give same result), and the profiler trace.

Thanks

Stored Procedure
================================================== ==============
ALTER PROCEDURE [Purchasing].[ntp_PurchaseOrderDetail_Insert]
(
@PurchaseOrderDetailId int OUTPUT,
@PurchaseOrderId int ,
@OrderQty decimal (11, 4) ,
@VendorProductId int ,
@Description nvarchar (255) ,
@UnitPrice decimal (18, 6) ,
@PackingQty decimal (14, 4) ,
@DueDateValue nvarchar (50) ,
@ModifiedDate datetime ,
@IsUnitPriceManual bit ,
@LineTotal decimal (29, 6) OUTPUT
)
AS
INSERT INTO [Purchasing].[PurchaseOrderDetail]
(
[PurchaseOrderID]
,[OrderQty]
,[VendorVendorProductID]
,[Description]
,[UnitPrice]
,[PackingMethod]
,[PackingQty]
,[DueDateValue]
,[ModifiedDate]
,[IsUnitPriceManual]
)
VALUES
(
@PurchaseOrderId
,@OrderQty
,@VendorVendorProductId
,@Description
,@UnitPrice
,@PackingMethod
,@PackingQty
,@DueDateValue
,@ModifiedDate
,@IsUnitPriceManual
)

-- Get the identity value
SET @PurchaseOrderDetailId = SCOPE_IDENTITY()

-- Select computed columns into output parameters
SELECT
@LineTotal = [LineTotal]
FROM
[Purchasing].[PurchaseOrderDetail]
WHERE
[PurchaseOrderDetailID] = @PurchaseOrderDetailId


Computed Column Formula
================================================== ==============
isnull(CONVERT(DECIMAL (29,6),[OrderQty]*([UnitPrice]*[PackingQty])),0.000000)
or
isnull([OrderQty]*([UnitPrice]*[PackingQty]),0.000000)

Profiler Trace
================================================== ==============
declare @p1 int
set @p1=115
declare @p16 numeric(29,0) <- should be numeric(29,6)
set @p16=5 <- value should be 5.259200
exec Purchasing.PurchaseOrderDetail_Insert @PurchaseOrderDetailId=@p1 output,@PurchaseOrderId=68,@OrderQty=4,@VendorProd uctId=28,@Description=N'93678975 - GL-2222',@UnitPrice=0.657400,@PackingMethod=N'Bags (2)',@PackingQty=2.0000,@DueDateValue=NULL,@Modifi edDate=''2008-05-19 15:06:37:610'',@LineTotal=@p16 output
select @p1, @p16