Steps to reproduce:
- Attach an mp3 file or text file on a page.
- go to Search Page, and at the "Type" option, select Attachment
- leave the option for "File Type" to All
- Search using a part of your file name. You will see it in the results.
- filter for "File Type" and select Audio or Text file. Search again. You will get no results.
It seems that ATM, there is no option to filter by file types.