eM Client v8 doesn't prompt for key passphrase

Hi,
I am running latest eM Client version 8.0.2951. I have installed a valid key set into the application with private key protected by a passport. The setting “Remember entered key passphrase” is set to “Never”.

When writing new email and selecting “Sign”, there is no prompt popping out and the message is sent out with invalid signature.

Any advice?
Thanks