Why does domain mapping force http

Why is it that when I go to type in a non-admin location of one of my mapped domains that is set up for https, ie: https://www.mymappeddomain.biz it will change the https to http?

I am thinking this is the reason my marketplace ecommerce plugin can not check out and is causing a redirect loop. Using ngnix, please advise. Note this issue does not occur on the blog 1, non-mapped domain.