Excel 2007 Pastes non existent pictures of arrows
 

When I do a simple copy and paste from a cell in one workbook to a cell in
another, Excel 2007 often (but not always) pastes 1 or more pictures into the
top left corner of the cell. These pictures are of arrows and sometimes 3 or
4 will have been pasted one on top of the other onto the cell

I have no idea why this is happening, but it is extremely annoying. Does
anybody know how or why this happens and how I can stop it?