I have reported this on the WaveLab forum. PG recommended that I report it here aswell. So here goes nothin'...
There is a problem that, as far as I can tell, only occurs with Yamaha badged plug-ins (sold by Steinberg). If a plug-in window covers any part of the waveform displays and the scroll button on the mouse is used to make settings, the waveform display beneath scrolls aswell! The problem occurs (at least) in the following plug-ins:
Vintage Open Deck
RND Portico 5033
RND Portico 5043
I haven't seen this problem with any non-Yamaha Steinberg plug-ins, nor any third-party ones. Furthermore, the problem does not occur in Cubase 7.
I haven't had the opportunity to try WL or WLE on a Windows computer, so I don't know if this problem is cross-platform or Mac only.