File upload issue with ALX extension and Document ID feature

On SharePoint Server 2010 with SP2 (14.0.7116.5000) with the OotB Document ID feature On, users upload files with extension ALX, using either the user interface or Windows explorer. Completed the upload, files become corrupted.

As a test I renamed some txt files to alx extension, to find that smaller files get appended the following HTML code:

TEST
TEST
TEST
TEST<!--[if gte mso 9]><xml><mso:CustomDocumentProperties><mso:_dlc_DocId msdt:dt="string">J55PMCUTTSQX-37-2</mso:_dlc_DocId><mso:_dlc_DocIdItemGuid msdt:dt="string">594c9167-dd94-4a94-8c15-c2f82eefcc0e</mso:_dlc_DocIdItemGuid><mso:_dlc_DocIdUrl msdt:dt="string">http://sharepoint/_layouts/DocIdRedir.aspx?ID=J55PMCUTTSQX-37-2, J55PMCUTTSQX-37-2</mso:_dlc_DocIdUrl></mso:CustomDocumentProperties></xml><![endif]--></head>

Tried again on a newly created site collection, with the Document ID feature disabled, and files were uploaded sucessfully.
I've noticed on a site collection where the Document ID feature had been enabled, it's not anymore, but the Libraries still keep a Document ID column, the problem is present.
I'm trying to figure out if anyone else suffers from this condition. If you don't, and you're sure Document ID feature is working properly, please let me know.

Thanks.