Annoying picturebox paint problem

[Doorstep]

Hi all, I've been trying to figure this out for a week now, but to no avail. Could someone please take a look at the included project? Basically, what I'm trying to do is paint bitmap images on an image bound to a picturebox, which in turn is on a tabsheet, which in turn is on a form. I can paint the bitmaps just fine, but when I minimize the app the image in the picturebox is the same as when I started. In other words, I lose any bitmap images I painted overtop . Any help on this is very much appreciated.

Thanks in advance