uploading new word 2007 documents

Hi ALL,
When i uploaded a docx (word 2007) documents it isn’t saving the document extension.
And when we are downloading the same file it is not recognizable be the operating system unless we have rename the file and added an extansion after we saved it on my comp.
if we will try it with doc (word1997-2003) documents it works fine…
Regards,
Liran