TeamSpeak mutes other applications

As soon as I start TeamSpeak other applications (e.g. FireFox, VLC Player, ...) gets muted. Additionally, these applications get muted again (after I un-muted them manually) from time to time while TeamSpeak is running. I know that I had the same problem with older versions of Mumble. I remember some Mumble-dev stating that Mumble once was registered as "phone application", thus the PulseAudio or so mutes other applications while "phone applications" are running. Newer versions of Mumble do not have this issue, because they are running as "Games" or something like that. However, like always, the TeamSpeak devs are not helping at all. Hence, I thought maybe I can force PulseAudio to stop this stupid auto-muting. Does somebody know if PulseAudio can be configured to stop auto-muting applications when "phone applications" are running? Or generally turning off any auto-mute functionality? I want to *always* control volume/mute myself.