Enter key not working on export

I set up a shortcut to export for export. (This may be irrelevant - selection from the menu has the same behaviour.)
Shortcut or menu brings up the export form as expected with the export button as default.
tab tab space works as expected, the mouse works as expected, but the enter key fails.
Observed that the enter key changes the colour of the button, but takes no action to the next step of export.