Curve adjustments no longer accurate. Photoshop self corrects.

When I use the curve or level adjustment adobe "corrects" it. For instance, I'm trying to grab all the shadows. The curve makes the channel nearly black and white. When I hit okay, the result it less of a contrast than I intended. The last 6 years I've been using this professionally it has never happened. GIMP can pull this off. Please tell me there is a quick fix. Very contrasty curves are used to isolated different areas for selections. This is a production stopping bug.

I have an image I can upload if the above explanation is not enough.