MVC FileResult With Specific Filename And Safari Or Chrome?

I'm having problems with FileResult returning a file with a specific filename. In the database the filename is just and ID + extension (e.g: 456789.mp3)

This piece of code

FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
return File(fs, "application/octet-stream", "myfile.mp3");

Work well in every browser except Webkit browsers (Chrome, Safari). Chrome and Safari receive files as original filename (456789.mp3). When I add headers with

Response.AppendHeader("Content-Disposition", "attachment;filename=myfile.mp3");

Safari receives the file as myfile.mp3attach (notice "attach" appended to the extension?), however Chrome receives this file as myfile.mp3,attach (it appends ",attach" to the extension)