Still investigating…
I’m trying to understand. Found something strange again : Now it’s possible to switch directly from Properties to Outliner without going into the long push up menu (apparently called EditorType). I don’t know why, but why not 
So ok. That’s nice and all, now let’s see what happens if I split one of those (because I CAN, right ?) :
…whaaat !? More icons ! Why xD
That EditorType stuff is giving me headache, sometimes it’s there, sometimes it’s not x) I think this topic have been brought before but sorry, was too lazy to go and search in every topic :p (even though there’s not much lol)
I remember that for the 3D view it’s possible to bring it back by unchecking > Hide EditorType menu, but actually I end up doing that EVERY TIME I open BFA because I need it !!! Please bring it back 
If for example I have 3 panels, even if the 3 of them are all 3D views, well one of them don’t have the EditorType icon while every others have it. It’s just weird.