Maybe I'm not seeing what you're talking about. Are you referring to a recipe change or something else?
<return> to capture and close an entry works for me these ways:
In Recipe:
1) Add grain, change the default amount
2) Substitute grain, change amount
3) Double click ingredient, change amount
In Inventory:
1) Add grain to inventory from the master list
2) Double Click the ingredient, change amount
The only time I'm seeing something like what you've observed is when I use Ingredients > Add Grain.