The GPU is not working to detect the faces. Please double check to make sure that “Use graphics processor” is checked on in the Photoshop preferences. That will be under the “performance” section in the photoshop preferences.
If that is on then please reset the Photoshop preferences. Then restart the computer and then test again. You reset the Photoshop preferences under the General section in the preferences. Select Reset Preferences on Quit to to that.
If it still doesn’t work then I need to know these things.
Exact Photoshop version number
Exact Plugin version number
Windows or Mac
Graphics Card make/model
If Windows, have you updated the graphics card driver to the latest driver from the graphics card manufacturer?