Live preview still rereshes on useless events.
for exapmple when there is any change in render->sequence/output tab, it refreshes uselessly. When size of picture is changed while lock aspect ratio is checked it should not refresh.
There should be a difference between stay open and stay on top.
"Useless" refreshes are likely to remain in the final release. Although they can be annoying and waste some time, I think it would be difficult to fully eliminate them at this point. But there may be some improvement before release at least.