Yes, I think it is by design and, Yes, I think you can fill the whole area so that you do not have that problem of going to the next field. What I don't know is that if you do fill the whole area with spaces, what the end result would be. It could not hurt to try.

Edit:
Having gone back, removing the restrictions and trying to insert spaces to lengthen the form field...I have found (at least in my very minimal trial and error test) that you CANNOT lengthen the field with spaces. There may be some other method but, with my minimal experience in this area, I am not familiar with it. I would have to step back and let one of the more experienced users advise you on other methods. Sorry I can't help further.