Can confirm the same behaviour. Using LE-Bose QC35 II on Ubuntu 18.04.4 LTS.
Switching to A2DP stops the "Call from.." prompts on the headphones but it also then deselects it as an input device. (I think this is correct for A2DP).
Selecting HSP/HFP or going back and selecting Bose QC35 II as an input device (which has the effect of selecting HSP/HFP) means the "Call from.." prompt comes back.
Can confirm the same behaviour. Using LE-Bose QC35 II on Ubuntu 18.04.4 LTS.
Switching to A2DP stops the "Call from.." prompts on the headphones but it also then deselects it as an input device. (I think this is correct for A2DP).
Selecting HSP/HFP or going back and selecting Bose QC35 II as an input device (which has the effect of selecting HSP/HFP) means the "Call from.." prompt comes back.