There is a bug in some versions of the Platform Services for Flash Lite implementation on S60 5th Edition devices that causes a screen refresh error when instantiating a platform service and disabling the touch keypad. The screen area under the service security prompt dialog never gets refreshed. The fix for this in ActionScript code is make the fscommand2 calls after the service instantiation, such as in this example for integrating with the sensors APIs:
var sensors = new Service("Service.Sensor", "ISensor");
fscommand2("FullScreen", true );
The Flash Lite team is aware of the bug (and provided this fix,) so I'm sure the bug will be fixed in an upcoming version of the S60 5th Edition software.