hit 'I' key to open inventory only all pages.
hit 'C" key to open hero and inventory both at same time (for us that like the old way).
make both options available at npcs.
oh and while im at it another suggestion is to make one single inventory pane be linkable to a hotkey to open just that inventory page for the purpose of fast switching items in dungeons and bf etc.
so for example you could dedicate one single inventory bag to gear you need to switch out in a hurry and certain food pots etc and be able to set that to a key so that u press that key only that window opens thus eliminating cluttered windows taking all the screen space. oh and it remembers where you closed it last time and reopens to that spot.
best of both worlds +1
just a suggestion.