When a call is made, the app seldom hangs and exits with a note that stays too short a time to read and the calls goes on but there is no way to hangup or to press any key on the keyboard. It won't even exist the app, as it says that it is not possible to exit because there is a call ongoing and there is no option to force existing.
Potentially it is a very expensive and dangerous issue. Try to imagine you called an expensive service or call, and cannot hangup or imagine you called a number by mistake and cannot hangup...