Steps to reproduce.
1. Setup document library portlet in a page, add some documents using multiple file upload and classic file upload.
2. While adding documents with classic file upload give some title, which will be displayed in the search results.
3. Setup search portlet in a separate page, when you search for these documents you will see the documents uploaded with multiple file upload and classic file upload.
4. The documents uploaded with multi file upload will be shown with file name with extension as a link, where you can download with out any issue.
5. The documents uploaded with classic file upload will be shown with their title as link, when you try to download these documents they will not be downloaded as expected. Since the these documents doesn't have any extension they will downloded as system drive kind of icon they are unusable.
Let me know if you need any more information, I have tried this with lucen inbuilt functionality and solr search server also.
I am happy to contribute if you can let me know the areas of the code to be fixed.