I’m no expert, but I think this is just how the graphics are implemented. They use the shape of a square. If you look at the jet engine fans in IF they’re not exact circles and you can see the shape bounce slightly. That’s just the way it is, it’s not a bug.
Known issue reported before release. The prop animation is created on a square plane with an alpha channel (whatever that means). Thought it would be fixed. Maybe a harder fix than I thought 😊