I have a phone that has 2 intercom buttons and DND on busy is not activated. If the person at this phone puts an incoming call on hold it flashes the line button as it should. But if they page someone to call them on their intercom so they can then transfer the call, the person answering the page by dialing the intercom number gets a busy signal. What might be causing this? We want the intercom to ring while the call is on hold on the line button. Assistance is greatly appreciated!