Factorio Forums

See attachement, i have a section of horizontal belt, empty, vertical belt, empty and then again horizontal.

Starting to drag at the empty secion, going horizontal, i first get a new horizontal belt, this then gets replaced by 2 underground, but then 1 underground is removed when i drag on ?!?
Going from right to left, you start dragging at 1, going just horizontal, when you reach collumn 2 you get situation 2, at column 3 you get situation 3, but then at column 4 you lose the underground. That seems undesired, it's hard to keep the underground when you drag quickly.

(I think it tries to place a new underground at position 4, but does not because it's already occupied).

Mods: Basis, Quality, Space age, Elevated Rails.

I have something similar happen to me. I was dragging a belt over a bit of a messy part of my base but with room for undergrounds to be placed. Somehow the game decided that it had to break one of the existing underground belts while also placing a new underground in the wrong orientation.
This is the minimal reproduction scenario I was able to find:

Ah your first example is pretty crazy, could swear you had a screenshot of two different situations, but that's really what happens:
Starting to drag at the green one towards the red 6, you get the horizontal situations at the red 1,2,3,4,5 and 6.

I would have expected that after 4, the next placement would simply be a single new horizontal underground exiting eastwards at 5.

Exactly my experience too. I made screenshots but the "before" failed and I already exited the game. If you desire I redo screenshots, let me know.

This report only handles the issue in the OP, for the other issues see 116892, 118408, 118421, make new report for issues that do not have one yet.

This has been fixed for a while.