the box I just posted from Stonehenge, yes there's a very small but noticeable tilt. That's a google earth capture. The tilt is due to the road sloping downhill,
I think.
You're using one of the defaults in that pic, aren't you? That one would be an issue for Jorin...well above my pay grade. I make them, I can't program them!
Moving the horizon line can be done, but not once it's created. It has to be done prior to segmenting the pano image.
I frequently encounter issues with ballpark backgrounds. Most of the time, I open up the background image files and edit them so they're empty vessels. I also frequently have to blow the camera angles out so that I can see the whole playing surface.
I'm going to dive in and look at some of my self-taken ones. I work at keeping things level, but I may need to work harder. I may need to confine myself to flatter areas. I'll also try some of the non-google third party boxes to see if they suffer from this. There is definitely something going on. That's a very, very good catch!