With the 'offical build' of .20, I see expected behavior. For my self built version and the pre-built .21, it sometimes launches properly and the content fills my entire 1920x1080. Most of the time it does not. It almost feels like some sort of race condition. I didn't really mention it earlier as this is still the experimental branch and it is something I can easily mitigate with a couple of key presses after launch.
Now that you refresh my memory, no pun intended, I do seem to recall that this isn't new or specific to Cool VL Viewer. Thanks for the reminder.
BTW, on the matter of jemalloc, I did notice a bump in fps as you had indicated. It is nice.