Something I've not encountered before (using LR 3.4.1). Processed one image and changed it from landscape to a square crop. Selected other images, one at a time, and used 'Previous' to apply all of the Develop Settings. Could have used Sync, but I needed to adjust the crop window slightly for each image.
I found that I could move the image (or crop window) around on the secondary images, and that I could resize it using the top/bottom or side handles, but as soon as I attempted to move any of the corner handles it automatically altered to the original (landscape) orientation even though the crop icon was locked. When I went back and selected the 1x1 crop, it set it to the full frame size (vertical, anyway).