You have not provided any system info or other details nor exact info about your files. From hardware acceleration issues to a flaky crop size preset having become sticky to specific metadata in teh source files this could be anything.
Sorry. It's a iMac, 10.6.8 and I'm using Photoshop CS3.
There's nothing odd about the JPEGs at all. This morning's photos came in as RGBs and both were 100pi wide at 72dpi. I needed to size them to about 30picas wide at 300dpi and greyscale. I've done this thousands of times before and never had a single problem.