The first thing you need to consider is if you want to work with virgin territory or not. You can read up on virgin territory in the manual of course, and there are also at least a couple of threads on it either here in the Nuendo section or in the lounge.
If you’re kind of new to automation I would instead recommend turning virgin territory off. You do this by opening the automation panel and clicking on the settings symbol in the lower left corner, and deselect “Use virgin territory”.
When you’re NOT using virgin territory there will automatically be an automation node at the beginning of the timeline, and the automation line will continue from there to the end. Before you write any automation; if you change the fader level the entire line will follow, from beginning to end, and that first automation node will follow the fader.
As soon as you actually write automation - and it doesn’t matter if you put the track into automation write and write using the fader, or if you do what you did in your first post - you will “break” that automation line where you’re writing automation for as long as you’re writing automation. When your automation write stops; the fader will return to that automation “line” that was there from before.
Just turn off virgin territory and try it again and it should be visually clear to you how it works.
The short version (of the discussion about virgin territory) is that some of us don’t think it’s as useful as it could be, and that it’s a bit counter intuitive. Basically, whenever you “locate” to a position in the timeline the track’s volume will pick up the level of the automation node immediately to the left of that position. That could be right before where you located, or it could be the very beginning of the timeline. To some of us that’s not intuitive because the whole concept of it is described more or less as “there are no automation nodes so no automation is read by the track”, but that’s not true - it’s really only partially true AFTER you’ve located and press play at which point you can move your fader freely without it snapping back to some automation. But as soon as you stop playback or loop back it’ll read that previous automation node. So, less useful to some of us.