Upload library - file not uploading - Need help debugging

This may have something to do with how the file is being created:
https://phpexcel.codeplex.com/discussions/286296

(this link is just an example, several similar results can be found by searching for application/cdfv2-corrupt xls)

That thread you point is the only result I can find, but well, at least I know that the problem is the way that those files are being generated.
The thing is that I thought I could avoid or force the upload without this mime checking, but the only way possible is by setting allowed_types = '*', which is not an ideal thing

Enrique
https://beza.com.ar