Haven't tried green fields actually! I was playing during waiting for some calls, and every time a call came, i would exit the location. When i noticed that the money from first location was running out, i was curious to see what happens if i spend it all. I thought that if you 100% green fields then nothing drops from it! That's not quite intuitive that you can go there again. That probably solves the issue, though of course if played the right way this shouldn't be an issue to begin with.
I think the card can stay selected after an invalid move. There's no reason to unselect it automatically, since you'll just select another card regardless if its selected or not, and if you're not going to select another card, the first card is already selected. There's no benefit that i see with deselecting it after invalid move. Haven't thought about that part, but it seems logical, yeah, you're right!