I think I have discovered a bug...
Select an image with a '.' in its name
e.g. "Picture.Mine.JPG"
Right Click "Convert Image..."
Choose "Resize", "Custom Size", "Add Filename suffix", "write converted images to destination folder"
See result...
Instead of "Picture.Mine-YYYxZZZ.JPG"
you will get "Picture.JPG"
/me using version 8.1.0.8 Unicode