Bluetooth connection to Toyota Prius lost during first call

Pairing can be established, but then gets messed up as soon as it is used.

When making a call, there's no audio on both ends, and soon after the Prius thinks that no phone is connected.

Moreover, on the phone there now is no audio, even when making a normal call (away from the car, without using hands free)

Clicking on the loudspeaker icon during the call fixes that though, but this is awkward, as this has to be done during the call, as the loudspeaker icon is not available anywhere else.

phablet@ubuntu-phablet:~$ lsb_release -rd
Description: Ubuntu 15.04
Release: 15.04
phablet@ubuntu-phablet:~$ apt-cache policy bluetooth-touch
bluetooth-touch:
  Installed: 0.3.1
  Candidate: 0.3.1
  Version table:
 *** 0.3.1 0
        500 http://ports.ubuntu.com/ubuntu-ports/ vivid/universe armhf Packages
        100 /var/lib/dpkg/status

What I expected to happen:
  When making a call in my car, I should hear the other party, and the other party should hear me. The configuration of both the car's bluetooth stack, and the phone's bluetooth stack should stay sane. After getting out of the car, it should be possible to make normal calls using the phone's builtin microphone and earset.

What happened instead:
 I could not hear the called party, and the called party could not hear me. After the call, the car's bluetooth stack seemed messed up (claiming no phone was connected), and so was the phone's RF stack and audio.
A call away from the car had no audio either. Wifi no longer worked (until I disabled, and then re-enabled it). Phone stayed "non discoverable" in Bluetooth and stayed so even after reboot (red spinning icon next to "Not discoverable" label in Bluetooth settings kept spinning forever)