by your explanation, I hope that is not a bug. but i wish user can have an option to remove that mode.

I hope you understand the bug correctly which I want to tell. now you want to tell this is bug or programmers purposeful make this desition.

I don't know about this issue on the 2.79. but now I notice this on the 2.80.

try once more
step 1: orbit the viewport and go below or above the center of the cube by pressing Numpad 7 or shift 7.
step 2: goto fly navigation mode by pressing shift+`

note

now try to move on all directions with a mouse you can see the difference if you fell this is normal.. press 3 or 1 and go to the fly navigation do move the mouse. actually every view wants to work in the same way but it not.

i had seen the some blender file of film hero that is fully compatible only with eevee. if i open on the 2.79 it shows the nothing but the file is open with empty screen because that greease pencil tool can run only in eevee. but in my case the the screen didnt open at all.
jut blender crashes everytime when i open it

i dont know what option to choose for posting this on post.
the problem is i add 2 objects in screen. cube and cylinder. cube as dynamic paint canvas, cylinder as dynamic paint brush.
i use cloud texture with cell noise data base as the texture to displace it by displace modifier.
now the cylinder and cube coinsering area should be removed on the cube by the mask modifier.
that produce holes on cube
but the holes is avoided in blender 2.80 just render as simple cube with wire frame modifier added.