Can't receive calls and sms while Hotspot is active

[tuxboson]

Using 2 Sim Cards
Sim 1 for using telephone calls (Provider: Telering (Austria))
Sim 2 for using mobile internet (Provider: 3 AT; this Sim is a Data-Only Sim)

While activating Hotspot (using/sharing the internet using Sim 2) I cant receive any calls (number from Sim 1) or SMS. When calling me the caller always get a message from tel-provider: "The customer is currently not accessible...", it seems like the phone switched of. But I can make calls during the phone is in "Hotspot"-mode without problems.

Calls and SMS are related to SIM 1
Data is related to Sim 2 (is running in 2G/3G mode)

After ending Hotspot I am not reachable at all. I have to reboot (sometimes twice) to be accessible again.
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Using bq Aquarius E4.5 Ubuntu Edition
with
Ubuntu 15.04 OTA-8.5 20151210

Phone is runing as it was delivered, no developer mode
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Hope you find a solution, use the phone as mobile modem each day ...
Thanks