Alfresco changtes the mime type if no extension defined

Hi,

I upload a Word document test.docx into Share. Then I change the name to test (without extension).

Note: for some reason some users do this when uploading, I do not know exactly how.

When I then do an online edit of the document and save it, a new version is created but the mime type changed to Binary File (Octet Stream), and of course preview and editing no longer work.

Why does Alfresco change the mime type?

Thanks,
Patrick