Save Render Preset Doesn't Save Filenames

To reproduce:

• Create new scene
• Add any item onto scene
• Amend render settings to include (viewport of iray) - Render Type: still image, Render Target: direct to file, Image Name: any valid image name, Image Path: any valid image path
• File -> Save As -> Render Settings Preset -> Select File -> Ensure all properties checked -> Ensure compress file uncecked -> Click Accept
• View .duf in text editor
• The `renderImgFilename` property is not present
• Note: Same with the `renderMovFilename` and `renderSerFilename` is image series or movie render targets are selected

Has anyone else run into this issue?