This wouldn't be a problem if save/ready were farther apart. Could have avoided this confusion.

I see that I failed to respond to this earlier.

I know very little about coding, but if I understand correctly this feature is actually very hard to code due to the way it's set up currently. The string of code that determines retreat options is completely unrelated to the orders code. Can't explain it in more detail than that, due to limited knowledge.

Thanks for answering so quickly, I should have looked closer. Since that is the case, I would like to change this to a feature request. If there are no legal destinations for retreat, the disband option should be pre-set.

Yes, in rule-book press you can only choose to Ready instead of Save. You cannot Ready/Save until you choose legal orders. This is intended. If you do not submit orders, the default is executed.

What you missed is that the "retreat"-box is also drop-down. If you change it to disband (for the unit without a disband), your orders become legal and you can submit them to the site.

I recently created a screenshot for this due to someone asking the same question:
https://imgur.com/a/o94iKze

I'm currently playing a game where I was attacked in two places during the same round, forcing me to order two units to retreat. One hade no valid destination to retreat to, so its destination box was empty. The other had only one valid destination, so its destination box was pre-set to that destination. No selections could be made for either unit, which is fully reasonable and to be expected. The problem is that the "Ready" button was disabled (greyed out and unclickable, tried clicking it several times). This is with the "Rulebook press" rule set, so communication is disabled during retreats and there is no "Save" button. When the retreat-orders were executed, both units were disbanded, since no orders were handed in.

The game is still ongoing, link is below. I'm playing France and this was the retreats of spring, 1997.

http://webdiplomacy.net/board.php?gameID=229111