While apparently default button sets like ok/cancel pair or some other that has some additional over those have a default set automatically, so one can just press enter without mouse-clicking the button. But for more custom buttoms it seems that the default focus disappears, and hitting enter does nothing. At least depending on the entirety of the dialog, maybe it has some nonsensical focus on some other area where it doesn't really respond to "enter," like "--picture," maybe...
