Weird MP3 problem with SONAR X1 PE x64

Hello,

two days ago, I tried uploading an MP3 rendered with SONAR to www.indabamusic.com. Locally on my system, the file played perfectly fine, but when uploading it, the MIME type of tjat file was detected as "application/octet-stream" instead of "audio/MPEG". I first thought, it might be a file name or a bitrate limitation issue, but this was not the case.

Then, I exported a WAV from SONAR and converted it using REAPER, which funnily enough , like SONAR, also uses LAME to do the conversion. Strangely enough, the resulting file was then correctly detected as "audio/MPEG".

Does anyone have a clue why this might happen?