Steps to reproduce (on Windows)
1. Upload a document to the document library (for example a text document .txt)
2. Wait until preview image is generated
3. Copy webdav URL of the document
4. Open Notepad -> File open -> Paste webdav URL
5. Make modifications to the document
6. Save document, close notepad
7. New version of text document was created but still shows the old preview image. Preview will not be updated automatically.