My hint seems to help for dual screen modes and is only an addendum to Erics recommendation: My second screen was set to 1600x1200. I switched to 1280x1024. Now I can scroll through the applications now. No news to what Eric mentioned.
Now what seems to be interesting: ANY vertical resolution on the second screen, which is below 1200 works. Now comes the catch: if I change the vertical solution on the primary screen to 1200 (looks ugly on a 16:9 screen), then app scrolling still works. Then my last check was, to go back to the secondary screen and return to 1200 vertical. Scrolling is not possible any more. Maybe the developers read this and dive deeper.
It is not the change of resolution in principle, which allows scrolling, but you should not go to 1200 and beyond for the vertical resolution. For me it is a perfect workaround, but maybe others need the higher resolution.