timrod,
All versions of Excel seem to have immense trouble keeping track of the correct locations of objects when there are numerous objects on a page, and most especially when there are several small objects combined to form a diagram or picture. I run into this problem often when I am trying to build process flow diagrams for my mass and energy balances at work. One possible way to fix this is to form your shapes into the picture or diagram you desire, group them together into one object, then copy and paste to Microsoft Paint. Crop the image, add whatever additional cleanup, drawing & markup you want to add, then copy and paste back to excel as an image instead of several grouped shapes. The downside is that once you do this there is no editing the images, so you'll have to take that into consideration. If you are completely done with your layout then go for it, or simply do it to sections that are done to avoid having to spend an hour readjusting them.