In addition of Stephen Kitt's answer, you could consider (especially if you are a developer yourself, and if the program -file in your case- source code is not too difficult to understand) fetching the source code of that program (perhaps from your distribution) - since it is free software - and patching it, and also sending a patch.
If you took time to study the source code, you'll probably make a better bug report.
If you took more time to propose a fixing patch, you are likely to be considered more seriously (and IMHO you are acting more in the spirit of free software).
So use the freedom provided by free software: study its source code (freedom#1) and improve it (freedom#3).
Today it is very easy to publish (e.g. on github) your improved version and share it (freedom#2).
Be sure to have the latest release of that file program. Many distributions are not using that (and perhaps the bug in your distro has already been fixed upstream).