I have a file open with unsaved changed. Then the file changes in the background. When I get back to pl/sql developer, it asks if I want to discard or see differences. The difference viewer shows the current file on the left-hand side, and there the content shows exactly as in the editor. The file-content on the right-hand side however shows as single-byte character set. Ie a greek omega shows as "Ω".
This also means it flags lots of false changes for the file.
PlSql Developer 15.0.4.2064