Sgp311 + xposed + root on 4.3, also flickering keyboard.
Tried stock kb and touchpal X, both the same issue.
Doesn't seem to matter what app I'm using.
Very annoying but except this 4.3 is running nice and smooth.
Edit: Disabling HW overlays seems to have "fixed" the issue on my device.
Don't shoot me if it doesn't work for you but it seems to be working for me, at least for now.
If you want to make it persistent (it isn't by default): http://forum.xda-developers.com/show....php?t=1904827
Hope this works for other users.
Please hit the "Thanks-button" if my post helped you.