Right now the filepool only looks for extensions in the URL of a file, so if a URL doesn't contain the file extension then it's going to download the file without it. This causes some problems.

If an SVG file is downloaded without extension then it's not going to work.

For example, in quiz we can download the icons:

/theme/image.php/clean/core/1456928261/i/grade_incorrect

Also, in iOS we can't open files without extension, they aren't shown. The new Moodle versions add the extension automatically to the files, but I guess old Moodles didn't do that so we've found several Moodles with this problem.