Will try to list below some admin UI issues as I find them:
1) at the top-left there's a big image that even when replaced in the theme wil smaller one keeps on showing the same tall empty header that doesn't have much use above the menus
2) if user has smaller screen (e.g. admin is logging in via some tablet), the page doesn't show scrollbars, neither the UI resized to fit dynamically in the page, so with small notebook/tablet screens you can't see the bottom part of the screen (e.g. the pager at the grid of pages in the Pages menu)
3) the Pages on the menu should be a dropdown to also have option to add new page, similar to how Groups show a dropdown menu. Else at least at the Pages webpage it should have an Add Page (now has it only at the admin home screen)