Active System Box disappears when scrolling

Seems a scrolling bug has been reported some time ago. My ASB completely disappears, although it's 2048x2048. Is this fixed? It's not in the list of the latest build and at the moment I have to work with the first Flash update.

Another question about ASB. You may wonder why I have such a large box. I wanted to use it as an overlay which covers backdrops outside of the visible area when the player scales the browser window (like the "Ctrl +" combination in Firefox).

I always used a large AO which has a transparent area of the games' window size, so only the desired part of the playfield is visible and everything outside is covered. Unfortunately, this AO causes a massive slowdown when scrolling. Would it run faster when using an ASB instead?