This is a known bug; the best workaround at the moment is to go into the Preferences panel, Characters section and make sure your font is set to NSimSun. That should fix it.
If your font is already set to SimSun and you're still seeing this problem, I'm afraid the only fix right now is to run the handwriting recognizer in palette mode instead - tap-hold on the handwriting recognizer button and select "bottom" and that will bring up the handwriting recognizer as a panel at the bottom of the screen. You can also push the button at the lower-left corner of that panel to collapse it to a small bar at the bottom of the screen (which lets you draw characters anywhere on the screen).