File extension doesn't appear in the Export Document dialog

Steps to reproduce:

1. Open the file human_T1.fa.
2. Click on the document context menu "Export Document" in the project view. The Export Document dialog appears.
3. Press on the browse button. Select file location dialog appears. Set the saving file: "test" and click "Save".
4. In the "Save to file" field in the Export Document dialog path of the document "test" appears without extension.
But if you change a file format parameter the extension appears.