If something like this happens, I would recommend tho check fileencryption , fileformat and bomb in ViM.Compare both files, the one you edited with nano and the one you edited with vim. Open them with vim and check this:
:set bomb?This is the byte order mark. Usually set when you edit a UTF-8 file with notepad.exe on windows. I often had problems with that.
:set ff?Fileformat dos or unix. dos have different line endings than unix.
:set fenc?The fileencoding: perhaps one editor changes to latin1 instead of UTF-8.