IN CAR: SIM2 calls cann not be routed via car audio

STEPS:
Requirements: Aquaris E4.5 with 2 SIMs, 2nd phone, a car with blue tooth phone support (Seat Alhambra 2012 in my case)

1. Connect the Aquaris to the car (with two SIM cards, car kid shows the provider of the 2nd SIM card in the display)
2. From the second device call the number of SIM1
3. Phone & car sound rings and call can be taken

4. From the second device call the number of SIM2
5. Phone does ring but car kit not.

6. Call 2nd phone from Aquaris connected to the car with SIM1 (via the phone directly or using the car kit)
7. Normal behaviour with in car phone & audio system

8. Call 2nd phone from Aquaris connected to car with SIM2 (only possible dialling from the phone)
9. No sound on the phone, no microphone support

EXPECTED:
I expect that calls from SIM2 can be taken and performed as from SIM1

ACTUAL:
SIM2 seems not to work when phone is connected to blue tooth of car whereby SIM1 works flawlessly

VERSIONS:
OS-Build-Number: 25
Ubuntu-Image: 20150825.1