Have you tried a recent Beta version? There have been many optimizations to the way the sizing and scaling are handled. Not to mention, it's the new GUI, which is being actively tweaked and refined for the next big release. Be sure to leave feedback. But also give it time.
I downloaded Wavelab Cast, and I don't get the issues you experience in 10.02 BETA040. However, they sound totally familiar with how it used to behave in OBS before Tom tweaked the crap out of it. However, being an official Steinberg product (the creators of the VST standards) I would be freaking shocked if the same issue was the cause of OBS' issues.
edit: I want to admit I didn't press render, I only played back.