@PaulS: Thank you for your answer - I've figured the problem out, its what @Grumpy_Mike means ...
The reset occurs when the slave calls Wire.write method after calling Wire.beginTransmission(MASTER_ADDRESS). So i rebuild my code to have the "normal"/correct i2c workflow - only the master sends data via begin transmission and the slave answers if Wire.requestFrom is called. So everything works fine - Sadly its not so nice stateless and independet as originally wanted - but it don't crashes anymore.
Thank you very much for your supprt, @PaulS and @Grumpy_Mike.
Best regards,
André