Can't login with fingerprint when plugged in

I have my phone set to display a roaming clock when the phone is plugged in. When the clock is displayed and the phone is plugged in, the phone will not wake and login when I touch the fingerprint sensor. It does wake and login if the phone is not plugged in. I have to wake it with the power button and then it will allow me to use the fingerprint sensor to login. Is this expected behavior or is there a problem with my phone?

It would help to know which phone you have, since different manufacturers may have different behavior.