While I can't seem to reproduce FlowerThief's issue, I did manage to get a ghost idol stuck to my cursor that I can't do anything with:
I achieved this only with an autoclicker.
And I mean, she got real stuck. Only after selecting another idol through the single creation menu did I get rid of her.
Mebius_Tos' issue is very easy to reproduce though. To help clarify their images, as I assume they are Japanese and not confident enough to post in English, it's achieved by starting to drag an idol by leftclicking, then rightclicking them while still dragging them, hence adding them to the formation, leaving you with the idol still on your cursor, after which you can drag that one over to formation as well.
Very easy to reproduce.
ありがと Mebius_Tos
Grats on Calli and Milky Queen streaming the game btw, Sadambober. I'd imagine that got the game quite some traction.