Can't view/edit attachment files when attachments has uppercase special character in filename

Bug Summary:

Can't add attachment files when attachment contains uppercase special character in filename

Environment:

Confluence version 6.5.1, database postgreSQL 9.5

Bug description

It is not possible to view/edit attachment files (attachments) which have special uppercase characters (for example German "Ä").
Lower-case special characters like "ä" will not cause any problems.
Problem affect postgreSQL database when database was created by using "C" collation/character sets.
Confluence Encoding test will not show any warnings.

Steps to replicate

1. Create postgreSQL database with "C" collation encoding/character set

   CREATE DATABASE confluencedb
   WITH
   OWNER = confuser
   ENCODING = 'UTF8'
   LC_COLLATE = 'C'
   LC_CTYPE = 'C'
   CONNECTION LIMIT = -1;
   

2. Link Confluence installer to confluencedb database
3. Create Confluence page
4. Enter edit mode, instert to the page two attachments with following filenames:

• "Sample Ä character .txt"
• "Sample ä character .txt"

Expected results

Both attachments can be added to the page

Actual results

• "Sample ä character .txt" is added successfully
• "Sample Ä character .txt" is displayed as "unknown attachments"

Workaround

Change database collation/character set to utf-8 ot create new database with correct collation and move existing confluence data to new database