Hmmm......strange. First thing I would try is to remove the battery, turn on the power, then off and then reinstall the battery. If it still has the problem then give Yuneec a call.
i know this sounds off the wall but try cleaning the screen i remember one person that had a similar problem and some one posted him to clean the screen and it worked .
call Yuneec and explain what's going on and if the ST-10 is still under warranty send it back or try to buy a new one , sometime you can pick up a new one on Ebay cheap .