RadMap has a problem with sufficiently large shapes, where if you zoom far enough into the shape it disappears. You can observe this effect in the demo:
Zoom for example into East Area. When you reach the last 2-3 zoom levels from the bottom there is a high chance that the shape will disappear and you will see the map beneath without white overlay. Sometimes it disappears immediately, sometimes after you do something. For example, if I switch to a different application with Alt+Tab and back to IE the shape disappears with 100% probability.
The larger the shape is the more there are zoom levels from the bottom at which shape disappears.