In editor mode, when underground belts with only one entrance or one exit are aligned with a blueprint that also include underground belts, the blueprints reacts randomly with the existing belts.
This also work with copy/paste
This happen with any belts colors.
This also affects the preview of the blueprint with no concordance between the preview and the constructed belts.
In game, when I reproduce the same situation the preview is correct, the "gost" is wrong and the final build by robots is wrong too.
![Image](https://forums.factorio.com/images/ext/2b639902444def424ad9e09a3d75b652.png)
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![Image](https://forums.factorio.com/images/ext/15b76a290ba896427fe198e0ac26dee0.png)