Advertising on a single channel with S132

Hi, we are trying to disable 2 of 3 advertising channels on nRF52832 SoC with the softdevice S132 (1.0.0-3.alpha) installed. The example project ble_app_beacon works well and is the code base for us. To disable the channel 37 and 38 we added following lines at the end of advertising_init().

m_adv_params.channel_mask.ch_37_off = 1;

m_adv_params.channel_mask.ch_38_off = 1;

But then it denies to send something on any advertising channel. Is there a bug in the alpha version of the softdevice or are further things to do for disabling one or two channels?

Thanks in advance!