Hey, One of my players noticed this during tonight's session: when you are using alt + mousewheel to scroll, if you scroll out really quickly all the way, the map disappears. The quick method to do this is:
Make some kind of map.
Use the toolbar to zoom to 20% (this makes it more convenient, but you can use any starting zoom except 10%).
Press alt and crank your mousewheel down really fast.
Results: the map disappears, and you can't scroll back to it, you need to use the toolbar to set the zoom back to an appropriate level.
We're both using Win8 and Chrome.