Blur lowers resolution of uploaded photos?

[bangbang023]

I'm trying to avoid having the Facebook app installed, since I felt it was silly to only have it installed for the sake of uploading pictures, so I set up Blur with my Facebook account and, just today, uploaded a picture using it instead of the official Facebook app. To my surprise, it uploaded a much lower quality image than the original.

Why is the Blur app downsampling uploads? Is there a way to change this behavior?

Thanks in advance.