I know this is a really old issue, but I was just seeing this happen with a .dll. I was using a newer .dll by accident, and I needed to reference and older one because I wanted to hit production environment without dev code. When I tried to do that, it kept using the new dll, even if I completely closed and re-opened LINQPad. The only way I could fix was to dump out the CodeBase path (Local\Temp\LINQPad5\blah\shadow_blah), open the folder manually, and delete the entire folder so it would reload the .dll's fresh. Is that expected behavior?