Nope, it appends it to all file types. Doesn't matter if it is an mp3, jpeg, apk, zip, pdf... it does it on everything. I can choose jpegs via the Gallery fine, and mp3 if they are part of my music library, but nothing when browsing through files. I noticed the problem while trying to upload frog recordings to naherp.com. The mp3s I record do not show up in my music library, so I browse the files to find them.
A friend of mine has two HTC phones, and said the issue occurs there too. I tried submitting a bug with google, but the told me to contact the vendor of my phone. I figured I would try here for help.