MixMonitor audible periodic beep during recording

Asterisk 13.23

When calling MixMonitor with B(15) as an option for a channel, I can hear a periodic beep on all channels connected to it (as well as on the channel I am recording). But after I redirect all those channels to a conference bridge (ConfBridge application) I can still hear the beep on the channel I am recording; however, the beep no longer sounds on all the channels that are in the conference bridge connecting to it.

Possible bug, but throwing this out there in case anyone has any thoughts before I create an issue in the bug tracker.