It is 100% replicable:
In this case I’m describing, there is an accidental addition of an automation point (because the pointer automatically switches to the pen 
).
And then you can ‘undo’ the automation point, BUT THE FADER WILL NOT GO BACK TO ITS ORIGINAL POSITION !!!
It must not be true that it is not possible to restore the fader position! You sit on something like this for a long time, it’s about 0.2 dB. You can’t fix something like that ‘just like that’!
Video
Here is the description of the video:
Unsightly ‘solution’ from Cubase with the stylus:
I’m using the arrow to change some automation data in the arranger, then I accidentally move the arrow to the FX track above it - right on the line that separates the two tracks - and suddenly the arrow changes to a pencil and sets the entire track above it, in which no automation data has yet been written, to minimum with the fader.
**Error 1
The automation point that was set by mistake is not registered as such for the time being. The fader remains at the old position - but the automation track is already at the minimum. Only when you move the point again does the fader suddenly jump there.
Error 2:
It can no longer be undone!!! Neither with Arranger Undo, nor with Mixer Undo. To be precise: The newly set automation point in the track above (it is a line across the entire track with ONE point) disappears again, but the fader on the track now REMAINS at the bottom.