i connect via Bluetooth a plantronics bbtense headset
then
i go to sound settings
then
in "advanced"
i see that the profile is "off"
then
i select "a2dp"
then
ok
then
i disconnect headset
then
i connect headset
then
i go to sound settings
then
in "advanced"
i see that the profile is "off"

i don't get this problem with a Philips SHQ7300 headset

the difference between the two headsets : the plantronics one gets a sleep mode to save battery when headset is not on your head.
after connecting the plantronics one if i put it on my head then profile does not switch to "a2dp"