So I finally upgraded to 2.x branch. I've encountered few annoyances with the new UI so far but none are as bad as this issue that I'm having: I can't dismiss dropdown menu in Tags field.
Say you're editing metadata of a particular book (Edit Metadata dialog) and you tab to Tags field and dropdown menu appears:
How do you dismiss it? Pressing Esc cancels the whole Edit Metadata dialog. Pressing tab (hoping to get out of the field) just selects the 1st tag in dropdown and another tab inserts it into the field.
The only way to dismiss it is to click with a mouse outside of it. That means it's impossible to use the UI efficiently with a keyboard only.
A good fix would be to make Esc close the dropdown without closing the whole dialog.