The "pole" issue has been reported in the past:
http://www.fsdreamteam.com/forum/index.php?topic=4534.30it doesn't have anything to do with Addon Manager or scenery installation, it's likely a video driver problem/bug or a problem with an FSX tweak, some users in that thread reported they fixed it by uninstalling FSX SP2 and installing the Acceleration pack, which seems to confirm it's a video-related problem, perhaps uninstalling the SP2 and installing the Acceleration pack has reset some settings in the FSX.CFG, which cured the issue.
I was never able to replicate it, but I always use Acceleration pack, so it might be also an FSX SP2 bug.