Have you ever had a problem getting the crop marquee to stay where you want it. Especially if you are only cropping a small portion and the marquee is near the edge of the frame. You drag out the marquee and it snaps back to the edge of the frame. The reason for this behavior is that, by default, Snap is enabled and Document Bounds is selected. (Located in the View menu shown on the left. View > Snap.) To permanently disable that behavior you can click either Snap or Snap To > Document Bounds to remove the check mark and disable the feature.
But a faster way to work is to temporarily disable snapping by simply holding down the Control key while dragging the crop boundary. This will allow more accurate placement of the outline when placement of the crop is critical. So when you are trying to place the crop marquee near the edge of the frame and it jumps back to the edge; holding down Control and then dragging will enable you to place the bounding exactly where you want it and it will stay there. Give it a try.