This is by design. The comment forms have a submit button on the right and other buttons are centered. For quick reply that's 2 buttons (there's a full editor button too).
The forms aren't meant to be any kind of form builder system (there is a single body text, and no system for determining how to compose multiple fields into that body text), the auto including of the URL is just a niceity that we did not intend to be forced to be kept.
I do acknowledge these things can be improved, hence keeping this issue open as a design change request.
(Click to enlarge)
#3639 - Button spacing on feedback form
The forms aren't meant to be any kind of form builder system (there is a single body text, and no system for determining how to compose multiple fields into that body text), the auto including of the URL is just a niceity that we did not intend to be forced to be kept.
I do acknowledge these things can be improved, hence keeping this issue open as a design change request.