Odd File Saving

I created a file in Rhino and saved it. Then I closed Rhino. Rhino said I had an unsaved file and asked me if I wanted to save it. The file looks the same as the file I had just saved. For protection, I saved this with a different name. The first file is 127KB. The second file is 3.7MB. I rebooted and looked at the files and they appear to have the same contents.