Not sure if this is your problem specifically, but I've had a similar problem with the HMI not handling the transparent background selection in the way you might imagine it should. If you have Transparent Background selected, try unchecking it.
If that's not it, you might try loading the images in Microsoft Paint and saving them as .bmp images, then using those as your Binary Image / Switch. I generally do that most of the time anyway because I like to alter the images slightly to my taste.