Tile Map Disappearing

Ok, either I spent too much time at Woodstock or I'm not getting something, which in either case implies that the program TGB is perfectly fine and I'm an idiot. (Verified by my girlfriend, cat and chicken)

So, I created a tile map and then painted it with an image and all was wonderful. Then I clicked on "Save Layer" and when it saved, the tile map was blank again. It keeps doing this and I can't figure out why. Any ideas?