I've tried both the apt package and downloading directly from adobe, to be honest I don't remember if there was a difference in problems, or just the same set of them, either way it didn't 'just work'.
I went through a phase I tried installing everything under the sun and looked around quite a bit (the packages directly from adobe, different apt packages, random bash scripts I found online..) so I actually don't remember what I tested and didn't.
What I have _at the moment_ and doesn't work that well, I got through the 'flashplugin-nonfree' package which if I understand is the 'preferred' way to install flash on ubuntu 64.
It's not flashplugin-nonfree, as the x64 version is still a beta package available separately (but drastically better than the standard one on x64 machines).
I had definitely tried that before, recall issuing a 'mkdir .mozilla/plugins' & moving a .so in there.
Can't remember why I rolled that back and reinstalled it through apt thought.
Anyways trying it again nonetheless, the blinking is still going on with scrolling, going to see if performance/crashing at least improves.
In case of the package, which package exactly did you install?