I had a similar problem, with scenery. When I was adding a pirate ship(scenery piece, not the ride) once it added it when I was rotating the landscape. It didn't add the normal piece, but the washed out preview piece. It counted as part of the coaster too! I couldn't delete it, selecting it selected the coaster but I couldn't select the part and delete it like the rest of the track and station pieces. I had to save the whole thing with scenery(I wasn't about to start over again), which saved it as a normal piece, reload the whole thing, remove the piece and save again. Sheeesh!
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"Eject Goose, Eject!"