If the mouse hits the preview window (I.E. the preview window is over the building so the mouse hits it when you hover over it), the preview flickers like hell. You tend to notice this at higher preview window sizes as it makes it more likely for the mouse to hit it.

Second more minor issue is if you take the preview window up to one size then drop it back lower, you get a black box around the outside of the preview window until you save and re-load. Screenshot below. As it can be cleared by a re-load it's very minor but thought i'd mention it:

https://drive.google.com/open?id=1AyXT7YJuD02bxZYftyHhtqIzrrDT18lK