Keep field value when drag a' drop expression field


I would like to suggest to keep value on the field while dragging expression field like can be seen on following image:


Not sure if it’s a personal issue, but when I filled two first fields and started dragging expression, at first I didn’t know where I wanna drop the expression. I believe it makes the brain confused when something is missing what it does not expect. Believe that this would help to understand my point of view.

Thanks in advance,
Your Simon!

I have the same confusion sometimes.
Maybe having it give the color change but still keeping the value that is in it would be nice.