See first screen shot, I have to nudge the mouse to make that tooltip go away, if I nudge onto the Edit radio button I get what you see in the second screenshot.
I question the utility of the first tooltip in Edit mode.
I also question why the Lock checkbox and Edit radio button are even shown in Edit mode, they don't do anything useful. If I check Lock before I edit, then after saving the edits and returning to View mode the Lock checkbox will be unchecked. Bug, maybe - I don't make use of the Lock feature.
A single radio button is meaningless. so I assume Edit button is there as a hint as to which mode you're in -- in which case it doesn't need a tooltip. But getting into NV's Edit mode is hardly something anyone is going to blithely stumble into.
IMO, NV's navigation controls are unnecessary clutter in Edit mode.
If one uses them NV quite rightly asks if you want to discard the edits. If you do then you should have used the Cancel button, which will take you back to View mode.
If you want to keep the edits then you must use Save which will take you back to View mode.
If you click Down in Edit mode and discard the changes you end up in View mode for the next book - you could have done that by Clicking Cancel and Down.
See third screen shot.
BR