I’ve had a similar problem with Cubase since version 7 - which suggests that I must be doing something wrong as I’ve seen the same thing on 7.5 and now 8 Pro (and on 2 iMac’s so I know it’s not the machine).
Initially following the install of Cubase everything is good - the mixer Channel Strip controls are clearly visible and usable, but after a while (and I can’t put my finger on what triggers it) - I find that the controls in the Channel Strip become invisible - if I hover over them I can see a rectangular outline - but there is no control visible.
The EQ ones seem to be ok - but for Compressor, Limiter, Gate etc, no controls. I have to reinstall whichever version was the last one I downloaded to get them back.
Running on an iMac with Mavericks 3.4ghz Intel Core i5 with 16gb RAM.
Any help would be appreciated.