Thanks for the screenshot. It looks like the call is in voicemail mode, so the keypad and mute button are intentionally disabled. There is a bug in telephony-service that could set conferences as voicemail calls when the voicemail number isn't provided by the sim card, which explains the problem.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1398431 Title: Can't mute a conference call To manage notifications about this bug go to: https://bugs.launchpad.net/canonical-devices-system-image/+bug/1398431/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
