Since the arrival of Gnome3 and its Client Side Decorations widgets, some GTK3 apps look weird. That’s why we’ve had another re-merge with Light Themes and adding some specific Lubuntu fixes. These includes Geary full (theme and icons) support, CSD menus, CSD gradients, borders and miscellaneous colours.
Some things must be fixed yet, like toolbar icon sizes and some borders (we’re on it). The fixes have been uploaded to the main branch (in case you want to use our PPA) and as a standalone archive (for other Linux distros). As Lubuntu is on Interface Freeze stage, these late changes won’t be uploaded to Ubuntu’s main repositories for final release on Vivid Vervet, so you’d need to upgrade your theme if you want to fix it. Sorry for the annoyance.