A splitter can be placed over an existing underground belt. This does not remove the underground belt segment (does not go into inventory), and once the splitter is removed, the underground belt is still there.
Seems harmless, earlier versions might have this bug as well. I haven't tested saving the game with this.
[0.10.1][kovarex] Placing splitter over underground belt
Re: [0.10.1][kovarex] Placing splitter over underground belt
Hello, thank you for the report, it is fixed for 0.10.2 now