BuddyPress.org

But this is a result of your theme, it’s not the widgets fault! the widget has two very distinct conditions to fullfil, those are not the same in terms of generated markup and thus will display differently, if that upsets your theme then this is a result of the decisions made in the visual styling and need to be then adjusted or styled to account for that change, BP can’t and won’t provide that styling, it can’t tell what situation it’s markup generated from the widget will find itself in.

How would you want to deal with this? it’s a common style to have ‘boxes,boxes actually are a bad thing in certain respects as people the expect them to have a certain height which isn’t how web pages/ markup and CSS work.

If you want the login box area to keep same height then you will need to add a property to force that such as min-height: 300px or whatever unit of measure is preferable.