I can see that it isn’t what you want but it seems reasonable to me that it would do that. You’re moving the selected face. The diagonal edges are remaining unchanged so the horizontal lines have to move?
What would you think should happen? Do you get what you want if you hit Ctrl to start a new face.
Not moving, pulling with Push/Pull.
My walkaround is hitting Ctrl but then much cleanup must be done.
Best scenario is perhaps to break the lines and draw new ones from the endpoints in the direction of the pull ?( as in hitting CTRL but without the internal face and the additional edges created by it)
Yes. I know you’re using Push/Pull but the effect is that you are moving the faces and its bounding edges. SketchUp is just filling in the space behind the face.
Maybe the filling can be teach/taught (what’s the form for this verb for the future?) to do things in a different manner( as I said),not just moving the lines.
“Taught” would be the correct word there. 
So there’d be breaks in the horizontal lines. Would the horizontal lines get broken if the angle is 0, too?
Thanks!
I believe it would be better to have the lines broken in a horizontal situation too. But now it all depends on the algorithm it would be used.
This is what I would like to have in my model, but I believe that first scenario will be the most used.
I think the right answer depends on what you intended to model. What are the edges across the original supposed to designate, and why do you want to extrude just that portion of the sloped face (which doesn’t align with any of the edges)? None of the behaviors shown so far correspond to what I would assume is being modeled, that is, a wall built of horizontal boards.
It’s a part of a 3d puzzle.
The point is that when using push pull, the geometry shouldn’t stick like this, imo.
I can think of a bunch of cases where that would cause problems.
Respectfully, I don’t agree. SketchUp has no way to guess several aspects of your intent. It doesn’t know that those edges were supposed to be parallel, only that they terminate at vertices on the original sloping edge. So it tries to track those endpoints as the extruded edge containing them moves. It also has no way to understand that those previously connected edge endpoints should become “free”, terminating in the middle of a new face. So I don’t think this is a bug, I think it is a matter of you wanting SketchUp to read your mind. It can’t, so you have to do some extra work.
erm… I think that most folk have missed one fundamental point - what are those horizontal lines doing in the first place? It’s excess geometry that has no value:
- If it’s aesthetics, use a texture (there is a horizontal line texture built-in)
- If it’s to model individual boards, then model individual boards (that gives a whole suite of other problems)
- If it’s to give texture, then push/pull every alternate one or run a v-groove down each line. (again you will then have problems pushing this section if you do this)
The only thing I can think on where you would want lines like this would be if it’s to fill adjoining boards with different fills (and then you would probably make the shape and over-lay a grid rather than put the grid on before shaping the area.)
The horizontal lines simulates the boards, and will be used for engraving.
Usually I draw them after I finish the entire model. This time I went a bit ahead with some of the detailing and that’s how I got this scenario( It also happened on different occasions too ).
I believe that this behavior can be smoothed a bit if the lines will somehow break where the face was initially placed. See pictures above.