Run a trace on that table to see what is going on.

Is there a trigger on that table?

If 20 is a hard number then something like this will get you what you are after.

CREATE TABLE #cds (codes VARCHAR(10))

INSERT INTO #cds

...

There is no issue. This is the behavior of SQL Server.

What I have done in the past to make sql give up it's memory it has built up:

Run this...

I'd do it more or less like so:

CREATE TABLE #Product (Id INT, ProductName VARCHAR(50))

DECLARE @Id INT=6, @ProductName VARCHAR(50)='name 6'

;MERGE #Product AS Tgt

USING (SELECT @Id, @ProductName) AS Src (Id, ProductName)

ON Tgt.Id...