In lightroom, when you right click -> "edit in" -> "photoshop" if you accidentally have many images selected, photoshop will attempt to open them all and freeze up your computer. I've done this with over 25 images before and have to kill lightroom. Could you please put a warning dialog / cancel option if someone tries to edit more than say 5 images in photoshop. I have noticed lightroom holds group selections if you try to select a single image that is in the group you already have selected - i.e. it doesn't unselect all the other photos. This is usually how I get in this situation.