It will do that.... Your experience is certainly nothing out of the ordinary. I made a gib strip out of a piece of 1/16" x 1/2" CRS a few years ago, and milling the dovetail angle along one edge made it warp about half an inch over its length.
If you asymmetrically mill a piece of CRS, it's virtually guaranteed to warp on you. Stress relieving it first (as per Halfnut's suggestions) helps a lot.
If you have a critical job, it may be worth the extra money to buy a piece of stress-relieved low-carbon ground stock. Aside from not warping, it will almost certainly machine to a better finish than the typical commercial CRS.
[This message has been edited by SGW (edited 08-06-2001).]
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