Paint.NET :: Changes Not Being Shown?

Say for example, Im doing a new drawing. I make a layer for my "sketch" , I save, then I create a new one and add line art with the brush. I save and exit to continue later. When I open it up again , it shows only the "sketch" layer, and not the recent changes. At first I was weirded out and frustrated, then I noticed by re-starting or turning off and on the PC, it displayed the changes. Its been happening to everything now.. for example I add color to something, and once I close it and open again , it wont show the changes at all, Im relieved knowing that once I reset itll show. But its really uncomfortable, it might even be something with my PC and not Paint.NET itself. But it doesnt happen to anything else.