Selection marquee is offset

[Ghoul Fool]

Ok what [Dorothy Parker quote removed] is this?  The Photoshop selections seem to be one pixel out: This is a zoomed in view of a green square about 50 pixels wide, but is noticable at 25% scale.

Have tried adjusting cache levels to no effect. Graphics drivers are up to date.

[Myra Ferguson]

if you're making the selection with the Quick Selection Tool, try selecting the Enhance Edge option in the Options bar (Window > Options).

I only noticed the offset with that tool while Enhance Edge was not selected. Both the Object Selection Tool and the Magic Wand Tool made the selection all the way up to the edge.

[Ghoul Fool]

Not using quick selections. This is using a classic select all.  Either that or a rectangular, marquee section (no anti-aliasing, no feathering) from corner to corner. You can see the selection jump a (sub)pixel when the mouse button is released.