Why does my DECT handset sometimes starts ringing while I am using my Smartphone?

MobileDock is linked to the Smartphone like a Bluetooth Headset. Depending on used APP (Siri) and Smartphone it may happen that the audio is forwarded to the DECT system. In order to avoid this, Bluetooth has to be unlinked in advance as follows:

Leave the Bluetooth range. (Connection status is show on Smartphone)
Switch off BT on my Smartphone.
Push the on/off button on MobileDock. (all Smartphones will be unlinked!)