It sounds like the designer put a building where an ai aircraft normaly parks. He might have had ai traffic turned down when placed them, or the ai plane simply wasn't there at the time. When I did my Vancouver airport scenery i cranked up ai traffic, turned the sim speed up to 16x and sat back and took note of where all the ai aircraft park. I didn't place any buildings, but I did line up gates for the ai planes to park at and I didn't want my static aircraft to conflict with them.
If the designer included his email address, you might want to bring the problem to his attention so he can do an update. Failing that, I would uninstall the scenery.