MSExcel file with no extension is recognize as a MSWord file

Hello,

I have a MS Excel file without extension (no '.xls'). When I put this file in Nuxeo, it is recognize as a MS Word file.

If I have an import file (zip file) with a document. This document is a MS Excel file without extension for "filename" atribute. But the mime type of the document is declared as "application/vnd.ms-excel".
After import, I can view the document and it is an MS Excel file in Nuxeo. For example, I can open the document with LiveEdit and MS Excel allows me to edit the document.
But if I save the document, it becomes a MS Word file.
I don't understand why the file type has changed. I modify the file, so its type doesn't change.
I'm agree that the mime type must be retrieved when a new document is created, but why look for the mime type if it's already known ?

Sébastien

PS: To test, simply create a MS Excel file and save it. Then rename it and delete the '.xls' extension