Yes, for some including me it is a good thing the crop transfers into Camera Raw even for JPEGs. But the behaviour (if the JPEG is opened into Photoshop or ACR) is decided by Adobe Camera Raw, not PM. ACR just recognises the saved crop information inside the XMP. You just have to change Adobe Camera Raw preferences to Disable JPEG support. You must have had ACR set to Automatically open JPEGs with settings currently.