Restarting calibre passes filenames
If Calibre is restarted (by the Calibre process itself), all arguments passed to the original process are passed to the new process. This probably makes sense for options, but I don't think it does for files.
Steps to reproduce:
1. Start calibre by passing it an ebook (e.g. "calibre mybook.epub")
2. Modify a configuration variable which requires a restart (e.g. change the interface font)
3. Apply settings, and click "Restart calibre now"
After restart, Calibre will re-attempt to add the ebook that was originally passed.