Lexicon PCM and Slate FG-X graphical corruption in WL8/Mac

Hello - my two 10.8.3 machines are both showing graphical corruption of Lexicon PCM and Slate FG-X in WL8 (majority of the plug in window goes white whenever the window is opened or repositioned). Clicking on the lower left area of the window tends to restore it.

Both are working fine on WL7 on the same machines.