[Kovarex] [2.0.72] Underground belt gets instantly destroyed when upgrading with smart belt dragging

[Cwdr_9]

Mods: Space Age
Viewing Nauvis from Gleba, I discovered that dragging a belt and upgrading the underground, in this specific order for some reason, made the underground disappear. Undoing it just said, it was deconstructed. The underground is also destroyed.

To reconstruct:
It works on all planets (To avoid mods potentially messing with testing, I only tested Nauvis, Gleba, Vulcanus, Fulgora, and in space.)

Build two or more belts, with the corresponding underground variant next to it.
Hold a belt of a higher grade in the cursor. Then start dragging from any given belt, over to the underground, and then away, towards the belt you started dragging from. The underground will disappear, and if it had items on it, they go with it, while showing the flying text, as if it was deconstructed by hand, with the total showing 0.

Info/Quirks:
Attempting to reproduce it in the editor did not work. Either it is the lack of a character, or its instant build quirk. Nonetheless, just spawn in a character.
Command to spawn a character, and control it: /c game.player.character = game.player.surface.create_entity{name="character", position = {0,0}, force = game.forces.player}

If you undo it, it will display "Undo deconstruction of Underground Belt". If you instead of undoing it, deconstruct it, and then redo until you are at the original belts, and undo those as well, the upgraded underground belt's ghost remain.
If done with remote view (the map) it is removed. If done without it, i.e., with the character's cursor, it gets put into the inventory.

The belts must be real. The underground does not need to.
Showcase video attached, however, text is is in danish. Since I deemed it minor enough, I didn't bother changing it to English. If needed, I can submit it in English

[Rseding91]

Thanks for the report however I can not reproduce any such issue. Are you using mods? If so, does it happen without them enabled?

[Cwdr_9]

I listed Space Age at the top, so yes, there is mods.
Note: It is currently late for me, so I'll test tomorrow, and edit the reply

[Rseding91]

Sorry, by mods I meant player-created mods (from the mod portal). Can you please provide a save file and steps to reproduce the issue? It doesn't happen when I try to do what's shown in the video.

[Cwdr_9]

Originaly, I did have mods. I then disabled all mods, except for Space Age, and tried to reproduce the bug again, to ensure it was not abnormal behavior from the mods.
As for the steps, those I already included, as well as a video. But if you must insist:

Build two transport belts facing the same way.
Then, build an underground transport belt, in front of the two transport belts, that extends one tile.
Now, hold three fast transport belts in the cursor.
Start dragging the fast transport belts from the transport belt adjacent to the underground transport belt.
Move the cursor over to the underground transport belt, while still dragging.
Then move away from the underground transport belt, towards the, now upgraded, fast transport belt and transport belt.
The underground transport belt should disappear now.

[Rseding91]

Ah, I see now. It's a smart-belt building bug. I have smart belt building disabled in my settings. If I enabled it, then I can reproduce the issue.